CPI Inflation Calculator
Calculate the inflation rate between two periods using Consumer Price Index (CPI) values, or find the real value of money after inflation.
How to use this tool
- Enter cpi (start period), cpi (end period) and initial dollar amount in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your cumulative inflation rate and the full breakdown beneath it.
⚠ This tool provides general estimates for education only and is not financial, tax or legal advice. Figures may not reflect your situation — verify with a qualified professional.
Formula
Inflation Rate = ((CPIend − CPIstart) / CPIstart) × 100%
Adjusted Value = Initial Amount × (CPIend / CPIstart)
How it works
The Consumer Price Index (CPI) tracks the average change in prices paid by urban consumers for a basket of goods and services. The inflation rate between two periods is calculated as the percentage change in CPI from the start to the end period.
The inflation-adjusted value shows how much money is needed at the end period to have the same purchasing power as the initial amount at the start period. A positive purchasing power loss means prices have risen and your money buys less.
Worked example
CPI Rising from 100 to 115 on $1,000
- CPI start = 100, CPI end = 115, Initial amount = $1,000.
- Inflation Rate = ((115 − 100) / 100) × 100 = 15%.
- Adjusted Value = $1,000 × (115 / 100) = $1,150.
- Purchasing Power Loss = $1,150 − $1,000 = $150.
Prices rose 15%, so $1,000 of purchasing power now requires $1,150, representing a $150 loss in real value.
Common mistakes to avoid
- Using the wrong CPI series (e.g., CPI-W instead of CPI-U) for general purchasing-power comparisons, which gives slightly different results due to different population coverage.
- Subtracting CPI values instead of dividing them, producing the wrong inflation rate -- the correct formula is (CPI_end - CPI_start) / CPI_start x 100.
- Confusing the CPI index level with the inflation rate -- the CPI is an index number (e.g., 310), not a percentage; the inflation rate is the percent change between two index values.
Key terms
- Consumer Price Index (CPI)
- A measure that tracks the average price level of a basket of goods and services purchased by households, published monthly by the U.S. Bureau of Labor Statistics.
- Inflation Rate
- The percentage change in the price level over a given period, reflecting the rate at which purchasing power erodes.
- Purchasing Power
- The quantity of goods and services that a unit of currency can buy; it decreases as inflation rises.
- Real Value
- The value of money or an asset adjusted for inflation, allowing comparison across different time periods.
Frequently asked questions
- What is the difference between CPI-U and CPI-W?
- CPI-U (All Urban Consumers) covers about 93% of the U.S. population and is most widely cited. CPI-W (Urban Wage Earners) covers a narrower subset and is used to calculate Social Security cost-of-living adjustments.
- How do I find historical CPI values?
- The U.S. Bureau of Labor Statistics publishes CPI data at bls.gov. Monthly index values going back to 1913 are available for CPI-U as downloadable tables.
- Can this calculator compare prices across any two years?
- Yes. Enter the CPI for the starting year and the ending year along with the original dollar amount. The calculator shows the equivalent purchasing power in the target year.