How Long Will My Money Last Calculator

Retirement drawdown runway

Turn a monthly withdrawal into a clear timeline

Start with the amount available, enter only the monthly gap your savings must cover, then compare the modeled runway with your own target. Every result uses the assumptions shown beside it.

1
Set the balanceMoney available now
2
Enter the monthly gapSpending less other income
3
Compare the runwayTimeline, chart, and table

Your scenario

What should your savings cover?

Display currencyFormatting only; no exchange-rate conversion.

Balance and monthly need

These two numbers answer the main “how long” question.

Savings available nowThe amount available before the first modeled withdrawal.Monthly withdrawal from savingsYour monthly spending minus Social Security, pension, and other recurring income.

Find the right monthly numberMonthly spending − Social Security − pension − other recurring income = withdrawal needed from savings.

Target and assumptions

Use a target to see whether the entered withdrawal fits your timeline.

Annual return assumptionA constant nominal annual scenario divided by 12. It is not a forecast.

Target durationChoose the length of time you want the savings to support.YearsWhole years from 0 through 100.Additional monthsAdd 0 through 11 months.

When does the withdrawal happen?Timing changes how long each month remains invested.

End of monthReturn is modeled before that month’s withdrawal.Beginning of monthThe withdrawal leaves less money invested that month.

Included in this estimate

One starting balance
One level monthly withdrawal
One constant nominal return

Inflation, taxes, fees, deposits, and market swings are not modeled.

All entered money values must use the same currency.

Estimated money runwayEstimate up to date

How long the entered withdrawal lasts

23 years, 2 months

$100,000 lasts about 23 years, 2 months while withdrawing $500 at the end of each month at a constant 3% nominal annual return.

Target gap

The modeled runway is 1 year, 10 months short of your 25 years target.

Entered monthly withdrawal: $500.00
Monthly withdrawal for your target: $474.21
Balance at your target: $0.00

$100,000 starting balance3% nominal annual return25 years target

This is a smooth, constant-return illustration—not a safe withdrawal rate, market forecast, or guarantee.

Your balance over time

Projected savings balance

Follow the modeled ending balance until the estimated depletion point. Switch to the table for exact annual values.

Modeled ending balance Estimated depletion point

Horizontal guides mark $100.0K, $50.0K, and $0.0.

Retirement drawdown · one auditable monthly path

Turn a spending gap into a clear money-longevity scenario

This calculator follows one opening balance through equal monthly withdrawals. It answers two separate questions: how long the entered withdrawal lasts, and what level withdrawal mathematically fits a chosen target. Every result depends on the assumptions you can see.

Start with cash flow, not a percentage

How the calculator works

First isolate the amount your portfolio must supply each month. Then apply that level withdrawal to one starting balance using the declared return and timing. The calculator does not invent income, spending, or a “safe” rate.

Define the portfolio

Use a dated balance that is actually available for this drawdown scenario. Keep reserves and assets that will not be spent outside the opening amount.

Calculate the monthly gap

Subtract income that pays the same month’s expenses. The remainder is the recurring withdrawal—not the household’s full spending.

Compare duration and target

Read how long the entered amount lasts, then compare it with the payment that fits the target horizon under identical assumptions.

The most important input

Net portfolio withdrawal

Put every amount on a monthly basis and use one consistent tax basis. If $3,200 of spending is partly covered by $2,000 of Social Security, a $500 pension, and $200 of other income, the portfolio gap is $500.

Total monthly spending$3,200

Social Security− $2,000

Pension− $500

Other income− $200

Net portfolio withdrawal$500 / month

Count an income source only for months when it is expected to be available. If income starts, stops, or changes, split the plan into separate scenarios instead of averaging unlike periods.

Starting balance

$100,000

Enter only the portfolio dollars available for this withdrawal stream at the scenario start. Do not include a home, emergency cash, or an income benefit unless it will actually fund these withdrawals.

Monthly withdrawal

$500 / month

Use the recurring gap the portfolio must cover—not total household spending. Keep spending and income on the same gross or net-of-tax basis before subtracting them.

Annual return assumption

3% nominal

The calculator divides this entered annual rate by 12. It repeats that monthly rate every month, so it is a transparent scenario input rather than a forecast.

Target duration

25 years

This is the comparison horizon. It does not change how long the entered withdrawal lasts; it lets the calculator solve a second withdrawal that exactly fits the chosen number of months.

Withdrawal timing

End of each month

End-of-month timing applies one month of modeled return before cash leaves. Beginning-of-month timing removes cash first and therefore produces a different path.

Follow one case all the way through

The default $100,000 drawdown misses 25 years

With a $500 end-of-month withdrawal and a 3% nominal annual return, the smooth model reaches zero after about 277.605 months. The calculator reports 23 years, 2 months because it rounds the continuous result to the nearest month.

Entered withdrawal lasts23 yr 2 moabout 22 months short of the 25-year target

Target-fit withdrawal$474.21per month for 300 months

Modeled balance at target$0depleted before month 300

Constant-assumption balance path$100,000 → $0

Modeled balance
25-year target

$100,000

Start

$83,838

Year 5

$65,065

Year 10

$43,257

Year 15

$17,925

Year 20

Month 278

Entered monthly withdrawal$500.00

Withdrawal that fits 25 years$474.21

The checkpoint columns make the direction easy to inspect, but the calculator uses unrounded monthly values between them. The orange target marker is a horizon—not a promised lifespan or required end date.

Reproducible annuity arithmetic

The recurrence, first month, and final partial month

For end-of-month withdrawals, the month’s return is applied first and the level withdrawal is removed second. Full precision is kept between months; currency is rounded only for display.

B₀: starting balance
Bₘ: balance after month m
W: level monthly withdrawal
r: annual return % ÷ 1,200
n: number of monthly periods

Monthly rater = 3 ÷ 1,200 = 0.0025

End-of-month recurrenceBₘ = Bₘ₋₁(1 + r) − W

Balance after n monthsBₙ = B₀(1 + r)ⁿ − W[((1 + r)ⁿ − 1) ÷ r]

Duration when W exceeds modeled returnn = −ln(1 − B₀r ÷ W) ÷ ln(1 + r)

First month01

Opening balance$100,000.00
Modeled return: × 0.25%+ $250.00
End-of-month withdrawal− $500.00
Month 1 ending balance$99,750.00

Depletion boundary277 → 278

Month 277 ending balance$302.04
Month 278 modeled return+ $0.76
Available before withdrawal$302.80
Requested withdrawal$500.00

Month 278 cannot fund a complete $500 payment. The continuous solution is 277.605 months, which displays as 278 months.

Output map

How to read every result and graph

Begin with the duration status, then reconcile the target payment, chart endpoint, and scenario table. A clear result should tell the same story in numbers, labels, and visuals.

01 · Modeled duration

The main answer

This converts the continuous annuity solution to the nearest month. In the default case, 277.605 months displays as 23 years, 2 months.

02 · Duration status

Did the entered draw reach the target?

Read the status beside the duration. Here, $500 per month depletes before the 300-month target, so the 25-year goal is not funded under these assumptions.

03 · Target-duration withdrawal

The reverse calculation

This is the level payment that mathematically reaches zero at the chosen endpoint. The default result is $474.21 per month—not a personalized spending recommendation.

04 · Balance at target

The endpoint check

A displayed $0 means the modeled account depleted on or before the target. It is clamped at zero and should not be interpreted as an allowed negative account balance.

05 · Balance-path graph

Direction and depletion point

Use the vertical scale for currency and the horizontal scale for time. The bars show sampled balances from one smooth recurrence; they do not depict real monthly market volatility.

06 · Withdrawal comparison

Entered amount versus target fit

The bars compare the $500 entered draw with the $474.21 target-fit draw. They use the same balance, return, duration, and payment-timing assumptions.

Thirty-second result check

Confirm the withdrawal is the portfolio gap, not total spending.
Confirm the return is an assumption and the timing matches cash flow.
Compare modeled duration with the target in the same months or years.
Check whether the balance bars reach zero before the target marker.
Save the inputs with the result so a later comparison is reproducible.

One result is only a starting point

Stress-test the assumptions one at a time

The same $100,000 balance produces materially different durations when one input moves. These rows use the same calculator formula; values are rounded to its nearest-month display convention.

Default balance with varied withdrawal, return, or timing assumptions
Scenario	Inputs changed	Modeled duration	25-year target
Default	$500 · 3% · month-end	23 yr 2 mo	Before 25 years
Lower return	$500 · 2% · month-end	20 yr 3 mo	Before 25 years
Zero return	$500 · 0% · month-end	16 yr 8 mo	Before 25 years
Smaller gap	$450 · 3% · month-end	27 yr 1 mo	Reaches 25 years
Larger gap	$550 · 3% · month-end	20 yr 3 mo	Before 25 years
Cash leaves first	$500 · 3% · month-start	23 yr 1 mo	Before 25 years

Return pressure

Run lower and zero-return cases

A fixed average hides sequence risk. A lower constant rate does not reproduce a crash, but it shows how dependent the answer is on sustained growth.

Spending pressure

Rerun a larger portfolio gap

Test higher spending, benefit changes, and inflation checkpoints as separate withdrawal amounts. The calculator does not raise the payment automatically.

Cost pressure

State whether return is net of fees

Fees reduce the dollars left to compound. Document any adjustment to the return input; account-specific taxes remain outside this simple recurrence.

Time pressure

Extend the target horizon

Compare 25 years with a longer period without calling either a lifespan forecast. A target is a planning boundary supplied by the user.

Scenario mechanics, not individualized advice

What can change modeled longevity?

The formula has only a few levers. These are neutral ways to build comparison cases; they do not identify what any person should do.

B₀

Change the opening balance

Compare a later start date, additional savings, or a deliberately excluded reserve as separate, clearly labeled starting-balance scenarios.

Change the portfolio gap

Reconcile essential and flexible spending with verified income. A smaller net gap lasts longer mathematically; real tradeoffs require personal context.

Use realistic return cases

Compare multiple net-return assumptions instead of raising the rate to force a desired answer. Higher assumed return also generally means risks the formula cannot show.

Revisit timing and horizon

Model benefit start dates, spending phases, and month-start versus month-end cash flow separately rather than compressing changing periods into one average.

Know what the smooth path omits

Limits to keep beside the answer

Returns are smooth

The same monthly rate repeats. Real gains and losses arrive unevenly, and losses early in a withdrawal period can produce a materially different outcome even if a later average looks similar.

Withdrawals stay level

The entered dollar amount does not rise with inflation or change for healthcare, housing, travel, emergencies, or other uneven expenses.

Fees and taxes are not separate inputs

If the return is intended to be net of fees, that adjustment must be made before entry. Taxes depend on account type, basis, jurisdiction, and the household's facts.

Longevity is not predicted

A target duration is a user-selected horizon. The result does not estimate lifespan, survivor needs, long-term care, insurance outcomes, or an appropriate reserve.

Income must be entered indirectly

Social Security, pensions, annuities, and other income are not projected here. Their effect belongs in the net monthly portfolio withdrawal you derive.

Rules and objectives sit outside the formula

Required distributions, account restrictions, legacy goals, benefit rules, and investment suitability require separate analysis and current records.

Quick answers

Money longevity calculator FAQ

What does “how long my money will last” mean here?

It means the time for one opening balance to reach zero under a fixed monthly withdrawal, a constant monthly return derived from the entered nominal annual rate, and the selected beginning- or end-of-month timing. It is a deterministic scenario, not a probability of success.

Should I enter all of my monthly spending as the withdrawal?

Usually not if other income pays part of that spending. First subtract Social Security, pension, and other income that applies during the same month. Enter the remaining amount the modeled portfolio must supply. Do not mix after-tax spending with gross income without accounting for taxes separately.

Why is the default duration 23 years, 2 months instead of 25 years?

At 3% nominal annual return and end-of-month timing, $100,000 supports a continuous modeled duration of about 277.605 months at $500 per month. The calculator rounds that duration to the nearest month. A 300-month payment that exactly fits the same model is about $474.21.

Why does beginning-of-month timing shorten the result?

A beginning-of-month withdrawal leaves a smaller balance exposed to that month's assumed return. In the default scenario, moving the same $500 from month-end to month-start changes the rounded duration from 23 years, 2 months to 23 years, 1 month.

What if the withdrawal is no more than the modeled monthly return?

Under a positive constant-rate recurrence, the balance may not mathematically deplete when the withdrawal is at or below the opening month's modeled return and the payment timing supports that boundary. The calculator labels that case and caps the display horizon; it still does not establish real-world sustainability.

Does the calculator adjust withdrawals for inflation?

No. The dollar withdrawal stays level. To explore purchasing-power pressure, rerun the calculator with larger withdrawal gaps at later checkpoints; do not treat one level-payment result as inflation-adjusted.

Is the target-duration withdrawal a safe withdrawal rate?

No. It is the payment that exactly exhausts the entered balance at one endpoint under one smooth return assumption. It does not model return sequences, uncertainty, fees, taxes, lifespan, spending shocks, or personal suitability.

Keep adjacent questions separate

Use the tool that matches the next question. An accumulation result, withdrawal-duration result, and required distribution are different calculations.

Important limitations

How Long Will My Money Last Calculator uses the rates, dates, fees, and assumptions entered or explicitly cited by this formula. It does not replace a current quote, eligibility decision, filing calculation, contract, or professional financial advice.

Review the stated scope, calculation method, assumptions, supported inputs, and effective dates, and obtain qualified advice before using a high-stakes result.

This formula passed its registered engineering tests and is published under an explicit site-owner policy authorization. No independent expert, QA, editorial, legal, or third-party review is claimed. Verify consequential results with a qualified professional.

This subject may affect health, finance, tax, legal, or other consequential decisions. It has not received an independent domain-expert review; consult a qualified professional before relying on it.

Retirement drawdown · one auditable monthly path

Turn a spending gap into a clear money-longevity scenario

Start with cash flow, not a percentage

How the calculator works

Define the portfolio

Use a dated balance that is actually available for this drawdown scenario. Keep reserves and assets that will not be spent outside the opening amount.

Calculate the monthly gap

Subtract income that pays the same month’s expenses. The remainder is the recurring withdrawal—not the household’s full spending.

Compare duration and target

Read how long the entered amount lasts, then compare it with the payment that fits the target horizon under identical assumptions.

The most important input

Net portfolio withdrawal

Total monthly spending$3,200

Social Security− $2,000

Pension− $500

Other income− $200

Net portfolio withdrawal$500 / month

Count an income source only for months when it is expected to be available. If income starts, stops, or changes, split the plan into separate scenarios instead of averaging unlike periods.

Starting balance

$100,000

Monthly withdrawal

$500 / month

Use the recurring gap the portfolio must cover—not total household spending. Keep spending and income on the same gross or net-of-tax basis before subtracting them.

Annual return assumption

3% nominal

The calculator divides this entered annual rate by 12. It repeats that monthly rate every month, so it is a transparent scenario input rather than a forecast.

Target duration

25 years

This is the comparison horizon. It does not change how long the entered withdrawal lasts; it lets the calculator solve a second withdrawal that exactly fits the chosen number of months.

Withdrawal timing

End of each month

End-of-month timing applies one month of modeled return before cash leaves. Beginning-of-month timing removes cash first and therefore produces a different path.

Follow one case all the way through

The default $100,000 drawdown misses 25 years

Entered withdrawal lasts23 yr 2 moabout 22 months short of the 25-year target

Target-fit withdrawal$474.21per month for 300 months

Modeled balance at target$0depleted before month 300

Constant-assumption balance path$100,000 → $0

Modeled balance
25-year target

$100,000

Start

$83,838

Year 5

$65,065

Year 10

$43,257

Year 15

$17,925

Year 20

Month 278

Entered monthly withdrawal$500.00

Withdrawal that fits 25 years$474.21

Reproducible annuity arithmetic

The recurrence, first month, and final partial month

For end-of-month withdrawals, the month’s return is applied first and the level withdrawal is removed second. Full precision is kept between months; currency is rounded only for display.

B₀: starting balance
Bₘ: balance after month m
W: level monthly withdrawal
r: annual return % ÷ 1,200
n: number of monthly periods

Monthly rater = 3 ÷ 1,200 = 0.0025

End-of-month recurrenceBₘ = Bₘ₋₁(1 + r) − W

Balance after n monthsBₙ = B₀(1 + r)ⁿ − W[((1 + r)ⁿ − 1) ÷ r]

Duration when W exceeds modeled returnn = −ln(1 − B₀r ÷ W) ÷ ln(1 + r)

First month01

Opening balance$100,000.00
Modeled return: × 0.25%+ $250.00
End-of-month withdrawal− $500.00
Month 1 ending balance$99,750.00

Depletion boundary277 → 278

Month 277 ending balance$302.04
Month 278 modeled return+ $0.76
Available before withdrawal$302.80
Requested withdrawal$500.00

Month 278 cannot fund a complete $500 payment. The continuous solution is 277.605 months, which displays as 278 months.

Output map

How to read every result and graph

Begin with the duration status, then reconcile the target payment, chart endpoint, and scenario table. A clear result should tell the same story in numbers, labels, and visuals.

01 · Modeled duration

The main answer

This converts the continuous annuity solution to the nearest month. In the default case, 277.605 months displays as 23 years, 2 months.

02 · Duration status

Did the entered draw reach the target?

Read the status beside the duration. Here, $500 per month depletes before the 300-month target, so the 25-year goal is not funded under these assumptions.

03 · Target-duration withdrawal

The reverse calculation

This is the level payment that mathematically reaches zero at the chosen endpoint. The default result is $474.21 per month—not a personalized spending recommendation.

04 · Balance at target

The endpoint check

A displayed $0 means the modeled account depleted on or before the target. It is clamped at zero and should not be interpreted as an allowed negative account balance.

05 · Balance-path graph

Direction and depletion point

Use the vertical scale for currency and the horizontal scale for time. The bars show sampled balances from one smooth recurrence; they do not depict real monthly market volatility.

06 · Withdrawal comparison

Entered amount versus target fit

The bars compare the $500 entered draw with the $474.21 target-fit draw. They use the same balance, return, duration, and payment-timing assumptions.

Thirty-second result check

Confirm the withdrawal is the portfolio gap, not total spending.
Confirm the return is an assumption and the timing matches cash flow.
Compare modeled duration with the target in the same months or years.
Check whether the balance bars reach zero before the target marker.
Save the inputs with the result so a later comparison is reproducible.

One result is only a starting point

Stress-test the assumptions one at a time

The same $100,000 balance produces materially different durations when one input moves. These rows use the same calculator formula; values are rounded to its nearest-month display convention.

Default balance with varied withdrawal, return, or timing assumptions
Scenario	Inputs changed	Modeled duration	25-year target
Default	$500 · 3% · month-end	23 yr 2 mo	Before 25 years
Lower return	$500 · 2% · month-end	20 yr 3 mo	Before 25 years
Zero return	$500 · 0% · month-end	16 yr 8 mo	Before 25 years
Smaller gap	$450 · 3% · month-end	27 yr 1 mo	Reaches 25 years
Larger gap	$550 · 3% · month-end	20 yr 3 mo	Before 25 years
Cash leaves first	$500 · 3% · month-start	23 yr 1 mo	Before 25 years

Return pressure

Run lower and zero-return cases

A fixed average hides sequence risk. A lower constant rate does not reproduce a crash, but it shows how dependent the answer is on sustained growth.

Spending pressure

Rerun a larger portfolio gap

Test higher spending, benefit changes, and inflation checkpoints as separate withdrawal amounts. The calculator does not raise the payment automatically.

Cost pressure

State whether return is net of fees

Fees reduce the dollars left to compound. Document any adjustment to the return input; account-specific taxes remain outside this simple recurrence.

Time pressure

Extend the target horizon

Compare 25 years with a longer period without calling either a lifespan forecast. A target is a planning boundary supplied by the user.

Scenario mechanics, not individualized advice

What can change modeled longevity?

The formula has only a few levers. These are neutral ways to build comparison cases; they do not identify what any person should do.

B₀

Change the opening balance

Compare a later start date, additional savings, or a deliberately excluded reserve as separate, clearly labeled starting-balance scenarios.

Change the portfolio gap

Reconcile essential and flexible spending with verified income. A smaller net gap lasts longer mathematically; real tradeoffs require personal context.

Use realistic return cases

Compare multiple net-return assumptions instead of raising the rate to force a desired answer. Higher assumed return also generally means risks the formula cannot show.

Revisit timing and horizon

Model benefit start dates, spending phases, and month-start versus month-end cash flow separately rather than compressing changing periods into one average.

Know what the smooth path omits

Limits to keep beside the answer

Returns are smooth

The same monthly rate repeats. Real gains and losses arrive unevenly, and losses early in a withdrawal period can produce a materially different outcome even if a later average looks similar.

Withdrawals stay level

The entered dollar amount does not rise with inflation or change for healthcare, housing, travel, emergencies, or other uneven expenses.

Fees and taxes are not separate inputs

If the return is intended to be net of fees, that adjustment must be made before entry. Taxes depend on account type, basis, jurisdiction, and the household's facts.

Longevity is not predicted

A target duration is a user-selected horizon. The result does not estimate lifespan, survivor needs, long-term care, insurance outcomes, or an appropriate reserve.

Income must be entered indirectly

Social Security, pensions, annuities, and other income are not projected here. Their effect belongs in the net monthly portfolio withdrawal you derive.

Rules and objectives sit outside the formula

Required distributions, account restrictions, legacy goals, benefit rules, and investment suitability require separate analysis and current records.

Quick answers

Money longevity calculator FAQ

What does “how long my money will last” mean here?

Should I enter all of my monthly spending as the withdrawal?

Why is the default duration 23 years, 2 months instead of 25 years?

Why does beginning-of-month timing shorten the result?

What if the withdrawal is no more than the modeled monthly return?

Does the calculator adjust withdrawals for inflation?

Is the target-duration withdrawal a safe withdrawal rate?

Keep adjacent questions separate

Use the tool that matches the next question. An accumulation result, withdrawal-duration result, and required distribution are different calculations.

What should your savings cover?

Balance and monthly need

Target and assumptions

23 years, 2 months

How the calculator works

Define the portfolio

Calculate the monthly gap

Compare duration and target

Net portfolio withdrawal

Starting balance

Monthly withdrawal

Annual return assumption

Target duration

Withdrawal timing

The default $100,000 drawdown misses 25 years

The recurrence, first month, and final partial month

How to read every result and graph

The main answer

Did the entered draw reach the target?

The reverse calculation

The endpoint check

Direction and depletion point

Entered amount versus target fit

Stress-test the assumptions one at a time

Run lower and zero-return cases

Rerun a larger portfolio gap

State whether return is net of fees

Extend the target horizon

What can change modeled longevity?

Change the opening balance

Change the portfolio gap

Use realistic return cases

Revisit timing and horizon

Limits to keep beside the answer

Returns are smooth

Withdrawals stay level

Fees and taxes are not separate inputs

Longevity is not predicted

Income must be entered indirectly

Rules and objectives sit outside the formula

Money longevity calculator FAQ

Related retirement calculators

Important limitations

What should your savings cover?

Balance and monthly need

Target and assumptions

23 years, 2 months

How the calculator works

Define the portfolio

Calculate the monthly gap

Compare duration and target

Net portfolio withdrawal

Starting balance

Monthly withdrawal

Annual return assumption

Target duration

Withdrawal timing

The default $100,000 drawdown misses 25 years

The recurrence, first month, and final partial month

How to read every result and graph

The main answer

Did the entered draw reach the target?

The reverse calculation

The endpoint check

Direction and depletion point

Entered amount versus target fit

Stress-test the assumptions one at a time

Run lower and zero-return cases

Rerun a larger portfolio gap

State whether return is net of fees

Extend the target horizon

What can change modeled longevity?

Change the opening balance

Change the portfolio gap

Use realistic return cases

Revisit timing and horizon

Limits to keep beside the answer

Returns are smooth

Withdrawals stay level

Fees and taxes are not separate inputs