Inflation Calculator
See how inflation affects purchasing power over time. Calculate future prices or past equivalent values.
At 3% inflation, $10,000 today buys only $5,537 of goods in twenty years — and something costing $10,000 now will cost about $18,061 then, a 44.6% loss of purchasing power.
Calculator
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How This Calculator Works
Inflation erodes purchasing power over time:
Future Cost = Present Amount × (1 + inflation)^years
At 3% inflation, $1,000 today will buy the equivalent of $554 in 20 years.
Worked example
Using the defaults — $10,000 at 3% inflation for 20 years:
Compute the erosion factor. (1.03)^20 = 1.8061. This is the multiple by which prices rise over twenty years at 3%.
Project the future cost. $10,000 × 1.8061 = $18,061. Something that costs $10,000 today will cost about $18,061 in twenty years at this rate.
Invert it to measure purchasing power. $10,000 in twenty years is worth $10,000 ÷ 1.8061 = $5,537 in today's money. You lose 44.6% of your purchasing power over the period.
Apply the rule of 72. 72 ÷ 3 = 24 years for prices to double. That matches the 1.8061 factor at year 20 and the 2.0 factor at year 24, so the shortcut is accurate for rates in the 2–8% range.
The calculator above returns $18,061 for these inputs. The rule of 72 is an approximation; the exact doubling time for 3% is 23.45 years, computed as ln(2) ÷ ln(1.03).
What inflation does to $10,000 over time
The same starting amount, eroded at four different rates across four horizons.
| Horizon | At 2% | At 3% | At 4% | At 7% |
|---|---|---|---|---|
| 10 years | $8,203 | $7,441 | $6,756 | $5,083 |
| 20 years | $6,730 | $5,537 | $4,564 | $2,584 |
| 30 years | $5,521 | $4,120 | $3,083 | $1,314 |
| 40 years | $4,529 | $3,066 | $2,083 | $668 |
Each cell is $10,000 ÷ (1 + rate)^years. At 7% inflation for 40 years you retain less than 7% of your purchasing power — the reason long-horizon planning cannot assume a stable price level.
Common mistakes with this calculation
- Assuming the official inflation rate matches your personal basket. CPI measures a national average basket. If your spending is concentrated in healthcare, education, childcare or housing in a fast-growing city, your personal inflation rate may run one to three percentage points above the headline figure.
- Using a long-run average for a short horizon. A 3% average over thirty years contains years at 9% and years at 0.5%. Over a five-year horizon the variance matters more than the average, and planning around an average alone understates the bad cases.
- Forgetting that wages also rise with inflation. Purchasing power erosion describes a static income. In practice wages tend to track inflation over long periods, which is why the correct question is usually whether your income is growing faster or slower than prices, not whether prices are rising.
- Applying inflation to a mortgage payment. A fixed-rate mortgage payment does not rise with inflation. That is precisely what makes it valuable during inflationary periods — the debt is repaid in cheaper currency while the payment stays flat.
When this calculator does not apply
- The rate is held constant, which no real inflation series ever is. Actual CPI readings range from negative to double digits year to year.
- It uses a single national index. Regional and personal inflation can differ materially from the headline number.
- It does not distinguish between asset price inflation and consumer price inflation, which diverge sharply.
- It cannot model the effect of substitution, where consumers switch to cheaper alternatives as prices rise, which is built into how CPI itself is constructed.
- Real returns require subtracting inflation from nominal returns, and this tool does not compute investment performance.
Frequently Asked Questions
What is the historical inflation rate?
US inflation has averaged about 3% annually over the past century. Recent years have seen higher rates (4-8% in 2022-2023).
Why does inflation matter for investing?
If your investment return is 7% and inflation is 3%, your real return is only 4%. Always account for inflation when planning long-term finances.
Sources & Methodology
This calculator uses standard financial formulas. See our methodology page for the full formula derivation.
- Consumer Price Index US Bureau of Labor Statistics
- CPI Inflation Calculator US Bureau of Labor Statistics
- Inflation and Price Stability Board of Governors of the Federal Reserve System
- Consumer Price Index Detailed Report US Bureau of Labor Statistics
- Inflation Expectations Federal Reserve
Last reviewed .
Key takeaways
- $10,000 at 3% inflation becomes an $18,061 cost in twenty years, and its purchasing power falls to $5,537.
- The rule of 72 gives a fast doubling estimate: 72 ÷ rate = years to double.
- Over forty years at 7% inflation, less than 7% of purchasing power survives.
- Your personal inflation rate is likely to differ from the national CPI figure.
- Fixed-rate debt is the one asset that inflation actively helps you repay.