Keep CPI-U and a custom basket outside personal cost-of-living claims
CPI-U represents an urban consumer population and BLS methodology across items and areas. A custom fixed basket is transparent but not official: each percentage-point contribution is the item's cost change divided by the full earlier basket cost, so rows reconcile to the total, but the basket omits official sampling, weights, substitution, and quality adjustment.
A household's geography and consumption can differ greatly from CPI-U, while one dominant custom row can make a basket unrepresentative. For wages, leases, pensions, taxes, or legal obligations, verify the exact series, release, reference period, and governing document. This calculator is educational arithmetic, not a personal inflation diagnosis, forecast, or indexation ruling.
Use historical, fixed-rate, direct-index, and basket modes distinctly
Historical mode uses the published CPI ratio. Forward and backward modes compound or discount a declared fixed rate and are scenarios, not forecasts. Direct custom mode compares two positive, like-for-like index endpoints and reports total plus geometric annualized inflation. Fixed-basket mode holds quantities constant, prices the same bundle twice, and normalizes the earlier cost to a base-100 index.
Direct endpoints must measure the same concept, geography, population, quality, unit, seasonal treatment, and reference base. Annualization smooths the endpoints rather than recreating their path. An optional amount is multiplied or divided by the custom ratio for a bidirectional purchasing-power comparison. The shared currency selector changes symbols only and never performs foreign exchange.
To convert a declared nominal accumulation path into a separate future amount, use the future value calculator and identify whether its rate is an assumption or a separately sourced CPI result.
Choose a published CPI-U observation without interpolating a missing month
Historical mode uses BLS series CUUR0000SA0: CPI for All Urban Consumers, U.S. city average, all items, not seasonally adjusted. It supports published monthly observations and annual averages from 1913. A monthly index and annual average are distinct observations; selecting one must not silently substitute the other. The calculator should display the series, observation type, and dates with every result.
Only published values belong in the historical calculation. For example, an October 2025 observation that was not yet released in a dated snapshot must remain unavailable rather than being interpolated from September and November or copied from a forecast. Revisions and release timing require source-date discipline. The ratio of ending CPI to beginning CPI translates one money amount across the two price-level observations.
A household's own two-location spending comparison belongs in the cost-of-living calculator and should not be labeled CPI-U.
Read CPI tables and charts according to their observation rules
A monthly table can show index levels and year-over-year change only when the corresponding month one year earlier exists. A yearly chart should use annual-average CPI where available rather than arbitrarily selecting December. Those two displays answer different questions: monthly year-over-year movement versus calendar-year average price level. Neither should fill a missing observation with a straight line.
Total purchasing-power change is the index ratio minus one; an annualized rate is a smoothed endpoint summary. It does not reveal every monthly movement. Preserve the raw published index precision and round only output. A large historical dollar conversion is not evidence that every item rose by the same percentage.
When recurring cash flows must be separated from endpoint inflation, use the investment calculator and keep deposits or withdrawals out of the price-index ratio.