CPI Inflation Calculator: Value of Money Over Time

What the CPI inflation calculator shows

This CPI inflation calculator answers two closely related questions about the past. First, how much did prices rise between two months, for example over the last 12 months or since January 2020? Second, what is an amount from one month worth in the prices of another, for example what a salary from ten years ago is worth in today's money?

Both answers come from official data. By default the calculator uses the Consumer Price Index for All Urban Consumers (CPI-U) of the U.S. Bureau of Labor Statistics (BLS), with monthly data back to January 1913. You can also pick Germany, France, Spain, Italy or Ukraine, and the calculator switches to that country's national consumer price index and currency. The data are bundled with the page, so everything is calculated in your browser and nothing you enter is sent anywhere.

An official price index is useful far more often than it seems. It tells you whether a pay rise was a real rise or only a nominal one. It shows what old savings, the price of a house or a rent from years ago would amount to in today's money. It lets you compare the return of a savings account or a bond with the inflation of the same period. And it is the starting point for adjusting a contract or a rent, although those usually come with rules of their own.

In this guide:

• How to fill in the fields and read the results
• How inflation over a period is calculated, and why monthly changes are multiplied
• When to count Between months and when Months inclusive
• Which price index each country uses, and US inflation year by year
• Average annual inflation, purchasing power and a check on your pay
• Where the data come from, the missing October 2025 and amounts from before the euro
• Worked examples, common mistakes and limits

If you want to understand inflation itself first, read the basics article on inflation and why money loses value.

How to use it: country, months, amount

The Your numbers panel has six rows.

1. Country. The United States is selected by default. Switching the country updates the available months, changes the currency of the amount and clears any pinned scenario, because comparing dollars with euros makes no sense. The amount you typed stays as it is.
2. Counting. Two buttons: Between months and Months inclusive. Between months is the default, which matches how most then-and-now price comparisons work. The difference is explained below.
3. Start month. Pick a month and a year in two lists. The hint below the field names the earliest available month, and for the United States it adds that October 2025 is not available.
4. End month. It cannot be earlier than the start month: if you move the start month past the end month, the end month follows. The hint names the latest available month.
5. Amount is in prices of. Start month converts the amount forward into end-month prices. End month converts backward: it shows what your amount in end-month prices was worth in start-month prices.
6. Amount. $1,000 by default. The slider runs to 100,000, and you can type up to a trillion. On a phone the field has − and + buttons.

When you open the calculator, it shows the last 12 months of data. With data up to September 2026 that is September 2025 to September 2026: $1,000 becomes $1,037.38.

Reading the results

The headline is the equivalent amount, with a label that says exactly what was calculated, such as "$1,000.00 in September 2025 prices equals, in September 2026 prices". Five figures follow:

• Price index: the price level at the end of the period if it was 100% at the start. An index of 103.7% means the basket of goods and services cost 1.037 times as much;
• Inflation over the period: the same as a change, +3.7%. If prices fell, the number is negative;
• Average annual inflation: the equal yearly rate that would produce the same inflation over the period. For periods shorter than 12 months it shows a dash with the hint less than 12 months;
• Change in purchasing power: how much less the same amount buys at the end than at the start. With 3.7% inflation that is −3.6%, not −3.7%;
• Months counted: the number of monthly changes in the period.

Three tabs sit below. Chart shows how the equivalent amount moved month by month, with a dotted line for the amount you entered. By year splits the period into calendar years: for each one you see the months, the price change in that stretch, the change since the start of the period and the equivalent at the end of the stretch. By month lists every month with its index (previous month = 100) and the change since the start; it is available for periods of up to 360 months.

Under the results the calculator names the last month of data and the source. Pin to compare remembers the current calculation: when you change the months or the amount, the headline shows the difference against the pinned result. PDF saves the inputs, figures and the by-year table, and Reset restores the defaults. The How it's calculated section summarises the data and rounding. On phones and tablets the results live in a panel at the bottom of the screen, and Details opens the figures and tabs.

How cumulative inflation is calculated

A consumer price index is a price level relative to a base period. The CPI-U equals 100 on average over 1982–1984, and in September 2026 it stood at 336.940, so prices were about 3.4 times their base-period level. The level itself means little; what matters is the ratio between two months:

Price index = CPI(end month) ÷ CPI(start month) × 100%
Inflation over the period = Price index − 100%
Equivalent amount = Amount × CPI(end month) ÷ CPI(start month)

• to convert backward, into start-month prices, divide the amount by the same ratio instead of multiplying;
• the base year cancels out, so a rebased index gives the same ratio.

Some statistics offices, such as Ukraine's, publish month-on-month indices instead: each month's prices relative to the month before, with the previous month equal to 100. To get a change over several months, these are multiplied, not added, because each month's rise builds on the prices of the month before. The calculator multiplies them into a chain of levels in your browser and then takes the same ratio, so the method is identical for every country.

Two more figures come from the price index:

Average annual inflation = (Price index ÷ 100%)^(12 ÷ months) − 1
Change in purchasing power = 100% ÷ Price index − 1

The second formula explains why purchasing power falls more slowly than prices rise. If prices double, the index is 200%, and money buys 50% less, not 100% less. In the other direction, a dollar that lost half its purchasing power needs prices to have doubled, which is what happened in the United States between January 2000 and September 2026: the index for that period is 199.6%.

Between months or months inclusive

The two buttons read "from month A to month B" in different ways. Both are correct, but they answer different questions, and this is where most differences from figures you have seen elsewhere come from.

Between months compares the price level in the end month with the level in the start month. January to September is eight monthly changes: February, March and so on up to September. January's own change is left out, because January is the reference point. This is the right choice when an amount is tied to a specific month: a salary paid in September 2016, a price you paid in March, an account opened in May. It is also how most then-and-now comparisons work.

Months inclusive multiplies the monthly changes of every month from the first to the last. January to September is nine months, measured from the price level of the previous December. Statistics offices use this form for year-to-date or full-year figures: "since the start of the year" means "compared with last December".

The rule of thumb: for a calendar year, choose Months inclusive with January to December, or Between months with the previous December to this December. Both give the same index. For a single month's inflation, choose Months inclusive with the same start and end month.

Which price index each country uses

Each country in the list uses its national consumer price index, not seasonally adjusted, as its statistics office publishes it. The table shows what the calculator uses and from which month its data start.

Why not seasonally adjusted? Seasonal adjustment removes regular patterns within the year so that economists can compare one month with the next. When you compare real prices across time, you want the prices people actually paid. The BLS says that people who use the CPI in escalation agreements should typically not use seasonally adjusted indexes, and that unadjusted indexes are used extensively for escalation purposes.

Germany, France, Spain and Italy also publish a harmonised index (HICP) built to a common European method, which suits comparisons between countries. The calculator uses each country's national consumer price index instead, the series its statistics office publishes as the CPI, VPI, IPC or FOI. The Ukrainian series has a territorial note from its producer: data for 2014–2021 and January–February 2022 exclude the temporarily occupied territories of Crimea, Sevastopol and parts of the Donetsk and Luhansk regions, and from March 2022 they exclude the territories temporarily occupied by Russia and parts of the areas where hostilities are or were under way.

US inflation by year

The table below was calculated with this tool from the BLS CPI-U: each row compares December with the previous December. The last column shows what $1,000 of the previous December was worth in that December's prices.

The quiet years of around 2% before 2020 were followed by 7.0% in 2021 and 6.5% in 2022, the fastest December to December rises in this table. Over the whole nine years prices rose by about a third: the index went from 241.432 in December 2016 to 324.054 in December 2025, a ratio of 1.342.

To see the same for any year since 1914, choose Between months with December of the previous year and December of the year you want. The By year tab does it for a longer period at once, and By month shows which months contributed most.

Average annual inflation and purchasing power

Inflation over a long period looks large and is hard to compare with a yearly interest rate. That is why the calculator also shows average annual inflation: the steady yearly rate that would produce the same price rise over the same time. From January 2020 to September 2026, US prices rose by 30.6% over 80 months, which works out at 4.1% a year.

That is the number to compare with the rate your savings earned. If a savings account paid less than average inflation over the same period, after tax, your savings lost purchasing power even while the balance grew. The basics article on whether to keep money in a savings account looks at that trade-off, and the one on compound interest and the time value of money explains why small yearly differences add up.

Purchasing power mirrors inflation. If prices rose by 30.6%, the same amount buys 23.4% less. To keep its purchasing power, money has to grow at least as fast as prices, year after year, and compounding works on both sides: on prices as much as on savings.

An average also hides the path. The 80 months above include 7.0% in 2021 and 2.7% in 2025. The average is useful for comparison, but the By year tab tells the real story.

Did your pay really go up?

A nominal pay rise does not by itself make you better off. To find the real change, divide the growth of your pay by the growth of prices over the same period:

Real change = (New amount ÷ Old amount) ÷ (Price index ÷ 100%) − 1

Say you earned $50,000 a year in September 2016. Between months from September 2016 to September 2026 gives a price index of 139.6% and an equivalent of $69,780.64: that is what you would need now to buy what $50,000 bought then. If you now earn $75,000, your pay rose by 50% in nominal terms and by 7.5% in real terms: 1.5 ÷ 1.396 − 1. If you earn $65,000, that is +30% on paper but −6.9% in real terms.

The same check works for a pension, a rent, the price of a home or school fees. If the new amount is below the equivalent, it has lost ground to inflation. For pay, what matters in the end is take-home pay after tax, which may also have changed over the period.

Where the data come from and how often they change

All series are taken from the producers' own public data services, or from the Deutsche Bundesbank in the case of Germany, and bundled with the page. The line under the calculator names the producer, the series and its licence; US data are in the public domain, and the BLS asks to be cited as the source. The data are refreshed after new releases, so the latest available month can trail the calendar by one or two months. National statistics offices typically publish a month's index within a few weeks: the September 2026 indices of all six countries were available by late October 2026.

Old values seldom change, but they can. The Ukrainian producer states that data calculated and published earlier are not reviewed, while Insee marks some recent French values as revised. When a producer revises or rebases its series, the next data refresh picks that up, so a result for recent months can move slightly after an update.

The missing October 2025

The US series has one gap. The BLS could not collect October 2025 survey data during the 2025 lapse in federal appropriations and did not publish an October 2025 CPI-U; its data show a dash for that month. The BLS has also said that it will not publish 12-month percent changes for October 2026 for indexes where October 2025 data are not available.

The calculator handles this as follows. October 2025 cannot be picked as a start or end month, and in Months inclusive mode November 2025 cannot be the first month either, because its change would need October as a reference. Periods that pass through October 2025 work normally: from September 2025 (324.800) to November 2025 (324.122), prices fell by 0.2%. In the chart the month appears as a gap, and in the By month table October and November 2025 show a dash for their monthly change.

Why results can differ from headline figures

The most common reason is a different question. The headline US figure each month is the 12-month change: this month against the same month a year earlier. A figure for a whole year may instead be the change in annual averages, which compares the average of all twelve months with the previous year's average. The calculator does not use annual averages; for 2025 the BLS annual average was in any case computed without October. Choose the same months and counting method as the figure you are checking, and the results should match to the decimal shown.

Amounts before the euro and other currency changes

Price indices run on through currency changes, but an amount has to be entered in the currency the calculator works in. Germany, France, Spain and Italy adopted the euro in 1999 and introduced euro cash in 2002. For an amount from before 2002, convert it to euros at the fixed rate first: 1.95583 Deutsche Marks, 6.55957 French francs, 166.386 Spanish pesetas or 1,936.27 Italian lire per euro. When the start month is before January 2002, a note under the results reminds you of the rate. Spain's data in the calculator start in 2002, so the note never appears there.

For Ukraine, the hryvnia replaced the karbovanets in September 1996 at 100,000 karbovanets to one hryvnia, and the calculator gives the same kind of reminder for earlier start months. US dollar amounts need no conversion over the whole period back to 1913.

The calculator does not convert between currencies. Dollar savings lose value with US inflation, euro savings with the inflation of the euro country you look at, and exchange-rate moves are a separate matter.

Worked examples

The figures below are calculator results on data up to September 2026. Once newer data arrive, end months and amounts will change.

Historical vs future inflation: which calculator to use

KrokFin has three tools that deal with inflation, and each answers a different question.

The CPI adjustment calculator applies the price change from a base month to a target month to an amount, in full or only a share of it, the way many rent and contract clauses work. Use it when you need the adjusted payment rather than a general picture.

The inflation impact calculator looks ahead. You choose an expected yearly inflation rate, and it shows what your money will buy in the future and what return would make up for the loss. The average annual inflation from this calculator is a sensible starting point for that rate. To compare a savings account with investing after tax and fees, use the deposit vs investment calculator, and to set a savings target in today's money, the investment goal calculator.

Common mistakes

Adding monthly rates instead of multiplying. Monthly changes compound. Over a few months the gap is small, but over several years of high inflation adding understates the rise considerably.

Mixing up the two counting methods. Year-to-date and full-year figures are measured from the previous December. If you chose Between months from January, you left out a month. Check Months counted.

Confusing inflation with the loss of purchasing power. Prices that rose by 100% mean money buys half as much, that is 50% less, not 100% less. The calculator shows both numbers separately.

Stretching one month into a year. A 0.6% rise in one month does not mean 7.4% a year; the next months may be calmer. That is why the calculator does not compute average annual inflation for periods shorter than a year.

Applying the wrong country's inflation. Savings lose value with the inflation of their own currency. For dollars choose the United States, for euros the euro country you care about, and treat exchange rates separately.

Entering old national currencies as euros. For amounts from before 2002 in Germany, France, Spain or Italy, convert at the fixed rate first, or the result will be too large by that factor.

Using seasonally adjusted figures from elsewhere. Headline commentary sometimes quotes seasonally adjusted monthly changes. They will not match the unadjusted index this calculator uses for any single month.

Limitations and data updates

The calculator shows the change in the average level of consumer prices according to an official index. It does not know your own spending: if rent, healthcare or fuel take most of your budget, your personal inflation may have been higher or lower. It does not account for exchange rates, taxes, interest or investment returns. How inflation fits next to the risk and return of different assets is covered in the basics article on risk and return.

The data end with the latest published month, and the calculator does not forecast future index values. Results are rounded only for display: amounts to the cent, percentages to one decimal. The result is not legal or tax advice and does not replace a calculation that a law or contract requires.

If you are weighing where to keep money so it holds its value, the article on what bonds are is a good next read. For decisions about your own savings, debts or retirement, consider a qualified, independent financial adviser.