インフレ 計算機 - Price and Purchasing Power

インフレ is the rise in a price index or in a specific price over time, and it quietly changes what a salary, pension, or cash balance can buy. People often quote a cumulative increase as if it were an annual rate, or they ignore the drop in purchasing power that is the mirror image of that increase. The inflation calculator separates those ideas: cumulative inflation, the constant annual rate that would produce the same change, and the percentage change in purchasing power. Cumulative inflation is final value ÷ initial value − 1. Annualized inflation is (final ÷ initial)^(1/years) − 1, the geometric average. Purchasing-power change is 1 − final/initial, which is negative when prices rise. Optional start and end dates are for your records; the math uses the time-period field in years, so enter 5 rather than relying on the dates. Value change in currency units is also shown as final minus initial. A price that moves from 100 to 110 over five years is 10.00% cumulative inflation but only about 1.92% a year. From 100 to 125 over ten years, cumulative inflation is 25.00% and the annualized rate is about 2.26%, while purchasing power falls 25.00%. That is why a “25% over a decade” headline overstates the yearly pace households actually felt. CPI baskets, regional indexes, and quality adjustments can differ from the two prices you type. Hyperinflation, deflation, and mid-year timing are not seasonally adjusted here. Use official index values when you need a statistical inflation rate, and use this worksheet when you want the implied inflation between two known prices or balances. Households can also run the inflation calculator on rent, tuition, or a grocery basket they actually buy, which often diverges from headline CPI. Businesses can apply it to a unit cost to see whether a planned price increase merely restores real margin. Because purchasing-power change is the negative of the cumulative price rise, a 25% price increase is a 25% loss of purchasing power on that item. Keep the year count honest; stretching a two-year jump across ten years will understate the annualized rate.