Why Inflation Calculators Disagree
And how to tell which answer fits your question.
The Short Answer
Two calculators can both use official government data and still disagree, because they are answering slightly different questions. The two big differences are which price index they use and which period they compare.
Neither answer is wrong. What matters is which one fits what you're trying to work out.
Open the inflation calculator →Reason 1: A Different Index
"Inflation" isn't one number. Several official measures exist, each tracking a different basket of goods:
| Index | Measures | Typically used for |
|---|---|---|
| CPI-U | Prices paid by urban consumers | The headline US figure; most calculators |
| CPI-W | Prices paid by wage earners | US Social Security adjustments |
| Chained CPI | CPI-U, adjusted for people switching products | US tax brackets |
| PCE | A broader measure of consumer spending | The Federal Reserve's target |
| HICP | Harmonised prices across the euro area | The European Central Bank |
PCE generally runs a little below CPI, so a calculator built on PCE will show somewhat less inflation over the same years.
Reason 2: A Different Period
This one causes the biggest surprises. Some calculators compare annual averages: the average price level across a whole year. Others compare one specific month with another.
The gap can be large. For 2009, US inflation was −0.4% measured as an annual average, but +2.7% measured December to December. Prices fell sharply in late 2008 and recovered through 2009, so the averages barely moved while the year-end figure jumped.
So if one calculator asks for a month and another only asks for a year, expect them to differ, especially for years when prices moved quickly.
Smaller Reasons
- The latest year. Some calculators include a partial current year or an estimate, which moves as new months are published.
- Rounding. Index values are published to one decimal place, which can shift results by a few cents on small amounts.
- A different country. Converting pounds with a US index, or the reverse, gives a meaningless answer. Each currency needs its own country's index.
Which Answer Should You Use?
| Your question | Best fit |
|---|---|
| What's $100 from 1990 worth today? | Annual-average CPI |
| Has my salary kept up since I was hired in March 2019? | A month-based calculator |
| How did prices move over one particular year? | December to December |
| Is my personal cost of living up by the same amount? | No calculator can say; see below |
What the Calculator Here Uses
The Inflation Calculator uses annual-average consumer price indexes, the standard answer to "what is this old amount worth today". US dollars use the Bureau of Labor Statistics CPI-U from 1913 to 2025, the euro uses Eurostat's HICP, and the other eight currencies use the World Bank's consumer price index. It shows the source for each currency under the inputs.
On that basis, $100 in 1990 is worth about $245 in 2025, $100 in 2000 about $186, and $1 in 1913 about $32.40. A month-based calculator will give slightly different figures for the same years. That's the difference in method, not an error in either.
Why It Still Might Not Match Your Life
Every index measures an average basket across the whole population. If most of your money goes on things that rose faster than average, such as rent, childcare, insurance or tuition, your personal inflation is genuinely higher than the headline number. That's a limit of averages, not a flaw in the calculator.
Frequently Asked Questions
Why do two inflation calculators give different answers for the same years?
Almost always one of two reasons. They use a different price index, such as CPI-U, CPI-W or PCE, or they compare different periods, such as annual averages versus one specific month. Both choices are legitimate; they answer slightly different questions.
What is the difference between annual average and December-to-December inflation?
Annual average compares the average price level across all twelve months of one year with the average of another. December-to-December compares one month with the same month a year later. They can differ sharply: for 2009, US annual-average inflation was -0.4 percent while December-to-December was +2.7 percent.
Which inflation calculator is the most accurate?
Any calculator using official data is accurate for the question it asks. The better question is which fits yours. For what an amount from a given year is worth today, annual-average CPI is the standard answer. For a specific month, such as a salary from March, use a calculator that takes months, like the BLS one.
What data does the calculator on this site use?
Annual-average consumer price indexes. US dollar figures use the Bureau of Labor Statistics CPI-U from 1913 to 2025. The euro uses Eurostat's euro-area HICP, and the other currencies use the World Bank's consumer price index. The source for each currency is shown under the inputs.
Why does my own cost of living feel higher than the calculator says?
Because CPI measures an average basket of goods across the whole population. If your spending leans heavily on things that rose faster than average, such as rent, childcare or insurance, your personal inflation is higher than the headline figure, and no general calculator can capture that.
Can an inflation calculator predict future prices?
No. Calculators based on recorded data only compare past years. Any figure for a future year is a forecast built on an assumed rate, not a measurement.