Rule of 72 Applied to Inflation
Rule of 72 applied to inflation: years for price doubling at various rates
| Inflation Rate | Years for Prices to Double | Your Money’s Purchasing Power Halves In |
|---|---|---|
| 1% | 72 years | 72 years |
| 2% | 36 years | 36 years |
| 3% | 24 years | 24 years |
| 4% | 18 years | 18 years |
| 5% | 14.4 years | 14.4 years |
| 7% | 10.3 years | 10.3 years |
| 9% | 8 years | 8 years |
| 10% | 7.2 years | 7.2 years |
| 72% | 1 year | 1 year |
At 3% inflation (near Fed’s target): 72 ÷ 3 = 24 years for prices to double. A retiree at 65 planning to live to 89 will experience all prices roughly doubling during retirement. Their income must double over 24 years just to maintain purchasing power. This is why COLAs, inflation-adjusted withdrawals, and growth assets are essential throughout retirement.
Rule of 72 for Investment Returns: The Other Side
The Rule of 72 also applies to investment returns: at 7% return, your money doubles in ~10.3 years. At 10%, every 7.2 years. The race between inflation (halving purchasing power) and investment returns (doubling money) is the fundamental tension in personal finance. If you earn 7% on investments with 3% inflation: real return ~3.88%, doubling every ~18.5 years. Your wealth in real terms grows, but slower than the nominal return suggests.
The Real-World Retirement Application
At 3% inflation over a 30-year retirement: prices nearly double (3% × 24 = price doubles at year 24). Social Security COLA adjusts benefits roughly with CPI. A fixed annuity provides the same nominal payment in year 30 as in year 1 — worth half as much in real terms. This is why financial planners consistently warn against relying on fixed-income-only retirement strategies.
Calculate How Long Until Prices Double
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