How this calculator works
A consumer price index tracks the cost of a fixed basket of goods relative to a base period, so the ratio between two readings shows how much the general price level moved. Multiplying an amount by that ratio restates it in the buying power of the later date, and dividing reverses the adjustment. The result is only as good as the index you supply: national indexes are averages, and a particular household can face a different mix of prices. Neither figure is a forecast of future purchasing power.
Formula
Adjusted amount = amount × (CPI later / CPI earlier). The price-level change is (CPI later / CPI earlier) - 1, and the original amount is the adjusted amount divided by the same ratio. Both index readings must come from one series with one base period.
Worked example
An index of 100 in the earlier year and 130 in the later year gives a ratio of 1.30, so $1,000 at the earlier date is worth $1,300 at the later date. The price level rose by 30% over the interval.
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Frequently asked questions
Which index should I use?
Use one official series, such as a national consumer price index, and take both readings from that same series. Mixing a national index with a city index or two different base years makes the ratio meaningless.
Does this measure my own cost of living?
No. Official indexes track an average basket for a whole population, so your spending pattern, housing costs and travel can move differently. The result is an estimate of general purchasing power, not a personal budget.
What does a price-level change below zero mean?
It means the later index is lower, so the same money buys more goods at the later date. The tool reports the fall as a negative percentage rather than rejecting it.