How to calculate the inflation rate from CPI
To calculate inflation from the Consumer Price Index, use (CPI now − CPI then) ÷ CPI then × 100. With the US annual average CPI-U of 313.689 for 2024 and 321.943 for 2025, inflation in 2025 was 2.6%. Over ten years, from 2015 to 2025, prices rose 35.8%. Convert any amount between years with the inflation calculator.
The formula
inflation rate = (CPI₂ − CPI₁) ÷ CPI₁ × 100
CPI₁ is the index at the start, CPI₂ at the end. The CPI itself has no unit; it is a price level compared with a base period. In the US, the CPI-U (all urban consumers) uses 1982–84 = 100. The Dutch CPI uses 2015 = 100. The base does not matter, as long as both numbers come from the same series.
Example: one year
US CPI-U annual averages (Bureau of Labor Statistics):
- 2024: 313.689
- 2025: 321.943
(321.943 − 313.689) ÷ 313.689 × 100 = 2.6%.
Example: ten years
- 2015: 237.017
- 2025: 321.943
(321.943 − 237.017) ÷ 237.017 × 100 = 35.8%. Something that cost $100 in 2015 cost about $135.83 in 2025, on average.
Average annual inflation
You cannot divide 35.8% by 10. Inflation compounds, like interest. Use the geometric average:
average = (CPI₂ ÷ CPI₁)^(1 ÷ years) − 1
(321.943 ÷ 237.017)^(1/10) − 1 = 3.1% per year. Simply dividing by ten would give 3.6% and overstate the average.
US and Dutch inflation by year
| Year | US CPI-U | US inflation | Dutch inflation |
|---|---|---|---|
| 2016 | 240.007 | 1.3% | 0.3% |
| 2017 | 245.120 | 2.1% | 1.4% |
| 2018 | 251.107 | 2.4% | 1.7% |
| 2019 | 255.657 | 1.8% | 2.6% |
| 2020 | 258.811 | 1.2% | 1.3% |
| 2021 | 270.970 | 4.7% | 2.7% |
| 2022 | 292.655 | 8.0% | 10.0% |
| 2023 | 304.702 | 4.1% | 3.8% |
| 2024 | 313.689 | 2.9% | 3.3% |
| 2025 | 321.943 | 2.6% | 3.3% |
Sources: BLS (CPI-U, annual averages) and CBS (CPI, annual averages). The calculator uses these series, with 2025 as the latest full year.
Monthly figures and "year over year"
News reports usually quote the change in the CPI for one month compared with the same month a year earlier, the so-called year-over-year rate. That uses the same formula with monthly index values. Annual averages, as in the table above, smooth out seasonal swings and are better for comparing years or adjusting salaries.
Converting an amount between years
To express an old amount in today's money:
amount today = old amount × (CPI now ÷ CPI then)
$1,000 in 2015 × (321.943 ÷ 237.017) = $1,358 in 2025 dollars. Going the other way, $1,000 in 2025 bought what $736 bought in 2015. This is how economists compare "real" wages or prices across decades.
Your personal inflation rate
The CPI reflects an average basket of goods and services. If you spend more than average on rent, fuel or food, your personal inflation can be higher or lower than the headline number. A homeowner with a fixed-rate mortgage and a renter facing a large rent increase experience very different price changes.
Frequently asked questions
What is a normal inflation rate?
The US Federal Reserve and the European Central Bank both aim for about 2% per year over the medium term.
What is the difference between CPI and inflation?
The CPI is a price level; inflation is the percentage change in that level over a period.
What is core inflation?
Core inflation excludes food and energy, whose prices swing a lot. It shows the underlying trend more clearly.
Why does the calculator stop at 2025?
It uses annual averages. The average for 2026 is only known once the year is over.