Long-term planning

Inflation Calculator

Enter a starting amount, annual inflation rate, and time horizon to see its future equivalent cost and how much purchasing power is lost. Adjust the rate between 2% and 8% to compare how apparently small differences in long-run inflation compound into substantial gaps in real purchasing power.

Last reviewed May 14, 2026 by ToolSpilo Editorial Team.

Review method: Reviewed against BLS CPI methodology/data tools and Federal Reserve PCE inflation-target language; preserved the calculator formulas while adding constant-rate limitations.

For informational purposes only. Not financial, investment, or tax advice. Results are estimates based on the inputs provided. Consult a qualified financial professional before making financial decisions.

Calculator tool

How this calculator works

Use the explanation to understand the formula, assumptions, and practical limits behind the calculator result.

What Is Inflation?

Inflation is the rate at which the general price level rises over time, reducing what a fixed sum of money can buy. A 3% annual inflation rate means that something costing 100 today will cost approximately 134 in 10 years — the same money buys 25% less.

The Formula

Future equivalent cost (what today's amount will need to be to match buying power):

FV=PV×(1+i)tFV = PV \times (1 + i)^t

Remaining purchasing power (what today's amount will actually buy in the future):

PP=PV(1+i)tPP = \frac{PV}{(1 + i)^t}

Where:

  • PVPV — present value (today's amount)
  • ii — annual inflation rate as a decimal
  • tt — number of years

Worked Example

1,000 today at 3% inflation for 10 years:

FV=1,000×(1.03)10=1,000×1.3439≈1,344FV = 1{,}000 \times (1.03)^{10} = 1{,}000 \times 1.3439 \approx 1{,}344

You would need 1,344 in 10 years to match today's 1,000 in buying power.

PP=1,000(1.03)10≈744PP = \frac{1{,}000}{(1.03)^{10}} \approx 744

Alternatively: your 1,000 today will only buy what 744 buys now, in 10 years.

Important limitation: this calculator uses one constant inflation rate. Official inflation calculators use CPI index values for specific dates, so use the official CPI series when you need a historical, date-specific result.

The Rule of 72

A useful shortcut: 72÷i%72 \div i\% gives the approximate number of years for purchasing power to halve.

Inflation RateYears to Halve Purchasing Power
2%~36 years
3%~24 years
4%~18 years
6%~12 years
8%~9 years

Real Return vs Nominal Return

When evaluating investments, the real return (inflation-adjusted) matters more than the nominal return. The accurate formula is:

Real return=1+nominal1+i−1\text{Real return} = \frac{1 + \text{nominal}}{1 + i} - 1

Simple subtraction gives a close approximation at low rates but understates the gap at higher ones. At 10% nominal and 6% inflation: real return is 1.101.06−1≈3.77%\frac{1.10}{1.06} - 1 \approx 3.77\%, not 4%.

CPI vs PCE: Which Inflation Measure?

Two indexes dominate public inflation measurement:

  • CPI (Consumer Price Index): tracks price changes for consumer goods and services and is widely used for public cost-of-living references.
  • PCE (Personal Consumption Expenditures): covers a broader spending measure and adjusts more for substitution between categories. The Federal Reserve states its 2% inflation goal in terms of PCE.

CPI and PCE can diverge. Both use the same compound math in this calculator — only the input rate differs.

Historical Context

PeriodAverage US Annual Inflation
1913–2023~3.3%
1970–1979 (high)~7.4%
2010–2019 (low)~1.8%
2021–2022 (spike)~5.7%

For long-horizon planning, 2.5–3% is a reasonable central estimate for developed economies, with 1.5% and 4% as conservative bounds.

Frequently asked questions

What is the difference between CPI and PCE inflation?

CPI tracks price changes for consumer goods and services and is the most familiar public inflation index. PCE covers a broader spending measure and adjusts more for substitution between categories. The Federal Reserve states its 2% inflation goal in terms of PCE, while many consumer-facing tools use CPI.

For personal planning, the main point is consistency: use one index for the scenario and do not mix CPI, PCE, and personal budget inflation in the same comparison. If you need a historical U.S. result for exact dates, use official CPI index values rather than a constant annual rate.

How does inflation affect bonds and fixed-income investments?

Inflation erodes the real value of fixed coupon payments. A bond paying 4% annual interest when inflation is 5% delivers a negative real return of approximately -0.95% (using the precise formula: 1.04/1.05 − 1).

Treasury Inflation-Protected Securities (TIPS) adjust their principal for CPI, providing genuine inflation protection. Series I savings bonds also carry an inflation component. For fixed-rate bonds, the risk is not default but purchasing-power loss — especially meaningful for 10–30 year maturities.

Why can't I just subtract inflation from my investment return?

Simple subtraction is a common shortcut that works well at low rates but diverges at higher ones. The accurate real return formula is (1 + nominal) ÷ (1 + inflation) − 1.

Example: 10% nominal return with 6% inflation gives 1.101.06−1≈3.77%\frac{1.10}{1.06} - 1 \approx 3.77\% real return, not 4%. The difference grows with the rate: at 20% nominal and 15% inflation, simple subtraction gives 5% but the real return is only 1.201.15−1≈4.35%\frac{1.20}{1.15} - 1 \approx 4.35\%.

How do I account for inflation in retirement planning?

Use real (inflation-adjusted) returns rather than nominal in long-range projections. Assume 2.5–3% annual inflation over 20–30 year horizons — it is conservative without being alarmist.

Social Security benefits are CPI-indexed, providing partial inflation protection. For other income streams, build in an annual spending-increase assumption of 2–3%. The biggest inflation risk in retirement is healthcare costs, which have historically risen faster than general CPI — consider a separate, higher inflation assumption for healthcare expenses.