Inflation Calculator
Adjust an amount from one year to another at a chosen average annual inflation rate, with cumulative inflation and lost purchasing power shown alongside.
Equivalent value in 2025
209.38
- Original amount
- 100.00
- Time span
- 25 years
- Annual inflation rate
- 3%
- Cumulative inflation
- 109.38%
- Multiplier
- × 2.0938
- Purchasing power of original in 2025
- 47.76
100.00 in 2000 has the same purchasing power as 209.38 in 2025, assuming 3% average annual inflation. The amount is multiplied by (1 + 0.0300)^25 = 2.0938. Cumulative inflation over 25 years: 109.38%.
How to use this calculator
Type in an amount, pick the year it was set in, pick the year you want to convert it into, and enter the average annual inflation rate over that span. Setting the To year later than the From year computes the nominal amount needed to match the original purchasing power — the figure usually quoted as "in today's money". Setting the To year earlier deflates the amount, telling you what it would have been worth back then. The primary result is the equivalent value in the To year; the breakdown shows the time span, cumulative inflation, multiplier and the purchasing power of the original amount once you arrive in the To year. The formula is currency-agnostic — feed it dollars, pounds, euros, yen, rupees, anything — and the model is the textbook constant-rate exponential, not actual CPI lookup, so the answer is only as good as the rate you put in.
How the calculation works
Inflation compounds the same way interest does. Each year, prices rise by some percentage, and the next year's prices rise on top of those. After n years at an average annual rate r (as a decimal), prices have multiplied by (1 + r)ⁿ — the same multiplier you would apply to a savings account growing at r per year. So an amount A in the From year is worth A · (1 + r)ⁿ in the To year, where n is the year difference. If n is negative (To year before From year) the multiplier becomes a divisor and the figure shrinks — that is the back-cast you would use to ask "what would $100 today have been worth in 1985?" Cumulative inflation is the multiplier minus one, expressed as a percent: 50% cumulative means prices are 1.5× what they were. Purchasing power moves the opposite way: a 50% rise in prices means each unit of currency buys 1/1.5 = 67% of what it used to. This calculator works in constant rates because that is what you have data for when you do not have a CPI series — for actual historical conversions, use a CPI table from your national statistics office and the same formula with the period rate replaced by the index ratio CPI(to) / CPI(from).
Worked example
How much purchasing power did $100 in 2000 have by 2025, assuming 3% average annual inflation? Enter amount = 100, from year = 2000, to year = 2025, rate = 3. The calculator returns 100 × (1.03)²⁵ = 100 × 2.0938 = $209.38 in 2025 — meaning you need $209.38 in 2025 to buy what $100 bought in 2000. The breakdown shows cumulative inflation of 109.38% and a purchasing-power figure of $47.76: $100 in 2025 dollars buys only what $47.76 bought in 2000. Reality check against the U.S. BLS CPI calculator with actual CPI data (CPI 172.2 → 313.7) gives $182.18 for the same conversion; the discrepancy is the difference between assumed 3% and the actual long-run average of ~2.4% over that window. Drop the rate to 2.4 and the calculator returns $181.04, within 1% of BLS.
Frequently asked questions
What inflation rate should I use?
For long-run averages: roughly 2.5% in the UK, 3% in the US, 3–4% globally, and 4–5% in many emerging economies. Central banks in developed countries target 2% explicitly (the Bank of England, the Federal Reserve, the ECB), and have hit that average over the post-2000 era give or take a percentage point. If you are converting across a window that includes the 1970s, the 2008 financial crisis or the 2021–2023 inflation spike, a single average will smooth over big swings — for high-stakes conversions, use an actual CPI series. The default 3% in the calculator is a reasonable "rule of thumb" for English-speaking developed economies over a multi-decade window.
Why does my answer differ from the BLS or ONS inflation calculator?
Official inflation calculators (US BLS, UK ONS, Bank of Canada) use actual measured CPI for each year, not a single average rate. They compute amount × CPI(to) / CPI(from). This calculator uses the constant-rate model amount × (1 + r)ⁿ, which is the smooth average. For a 50-year span the answers can be 10–30% apart even with a well-chosen rate, because real inflation is bumpy — high in some decades, low in others. Use the constant-rate model when you do not have a CPI series, when you want a quick rule of thumb, or when you want to ask hypothetical "what if inflation stays at X%" questions. Use an official CPI-based calculator when you need the historically accurate answer.
What is the difference between nominal and real value?
Nominal value is the face amount on the bill or contract — the number of pounds, dollars or rupees, taken at face value. Real value adjusts for inflation: how much that money would actually buy, expressed in some reference year's prices. This calculator converts between the two when you set one of the years as the reference. The "equivalent value in To year" is the nominal figure you need in the To year to match the From year's real purchasing power. The "purchasing power" row is the reverse view — the real value, in To year prices, of the original nominal amount. Salaries, contracts, pensions and historical statistics are almost always quoted in nominal terms unless explicitly flagged as "real" or "inflation-adjusted".
Does the rule of 72 work for inflation?
Yes — it is the same compound-growth formula. The rule of 72 says that prices double in roughly 72 / r years where r is the annual inflation rate in percent. At 3% inflation, prices double in about 24 years (72 / 3); the calculator gives 100 × (1.03)²⁴ = $203.28, close enough. At 6%, prices double in 12 years (72 / 6); the exact figure is (1.06)¹² = 2.012, again within 1%. The approximation is good for rates between 2% and 10%; it drifts at very low or very high rates. It is a handy mental shortcut for "how long until my money is worth half as much?" — at 3% inflation, 24 years.
How do I handle negative inflation (deflation)?
Enter a negative rate. At −1% annual deflation over 10 years, an amount of $100 grows to 100 × (0.99)¹⁰ = $90.44 in nominal terms — but its purchasing power increases, because prices have fallen. Deflation is rare in modern developed economies — Japan in the 1990s and 2000s saw small bouts of it, the US during the Great Depression saw deeper deflation. The model handles it cleanly because (1 + r)ⁿ is well-defined for negative r as long as r > −100%. Below −100% the formula breaks (prices would have to fall to zero or invert) and the calculator returns a validation error.
Can I use this for currency conversion across years?
Only if the conversion is in a single currency. The calculator does not handle exchange rates — it inflates or deflates an amount within one currency, using the inflation rate for that currency. If you want to compare $100 in 1990 USD against £100 in 1990 GBP, do this in two steps: inflate each to your target year separately using its own inflation rate, then convert at the current spot exchange rate (or a different one if you want to know what the exchange rate "should" be under purchasing-power parity). Cross-currency, cross-time comparisons are tricky and depend on whether you care about purchasing power, exchange-rate adjusted income, or something else — pick the question first.