How does inflation affect your money?
Inflation erodes purchasing power over time. At 3% annual inflation, $100 today will only buy $74 worth of goods in 10 years. To maintain real value, your investments must earn returns that exceed inflation. The "Rule of 72" shortcut: divide 72 by the inflation rate to find how many years until prices double.
Formula & Methodology
Future Purchasing Power
Future Power = Amount ÷ (1 + Rate)^Years The core formula. Divides by the compounded inflation multiplier to find the real value in today's dollars.
Cumulative Inflation
Cumulative = ((1 + Rate)^Years − 1) × 100% At 3.5% for 20 years, prices rise 98.9% — nearly double. This is why the "amount" you need in 20 years is almost twice today's price.
Historical CPI Adjustment
Adjusted = Amount × (CPI_end ÷ CPI_start) Uses official BLS CPI-U annual averages for precision. The annualized rate = (CPI_end/CPI_start)^(1/years) − 1.
Real Return (Fisher Equation)
Real Return = (1 + Nominal) ÷ (1 + Inflation) − 1 The true inflation-adjusted return. A 7% investment at 3.5% inflation yields a real return of only ~3.38%, not 3.5%.
Goal Planner — Monthly Savings
PMT = FV × r / ((1+r)^n − 1), r = monthly return, n = months Standard future-value annuity formula. Solves for the periodic payment needed to reach a nominal future goal.
Key Terms
- CPI-U (Consumer Price Index, Urban)
- The primary US inflation measure. Tracks prices of 80,000+ items for urban consumers. Published monthly by the BLS.
- Purchasing Power
- The quantity of goods one unit of money can buy. Inflation erodes it: $100 today buys less than $100 did 10 years ago.
- Deflation
- Negative inflation — prices fall, purchasing power rises. Rare in modern economies; historically associated with recessions.
- Real Value
- Nominal value adjusted for inflation. $10,000 nominal in 20 years at 3.5% inflation has a real value of only ~$4,975 today.
- Break-Even Rate
- The minimum return an investment must earn to preserve purchasing power. Equals the inflation rate exactly.
- TIPS / I-Bonds
- Treasury Inflation-Protected Securities and Series I Savings Bonds — government-backed instruments that adjust returns with inflation.
- Rule of 72 (Inflation)
- Divide 72 by the inflation rate to estimate years until purchasing power halves. At 3.5%: 72÷3.5 ≈ 20.6 years.
Worked Examples
Example 1: Retirement Planning
Scenario: You want $500,000 in today's purchasing power at retirement in 25 years. Inflation: 3.5%.
Nominal Goal: $500,000 × (1.035)^25 = $1,181,374. You actually need over $1.18M to have the equivalent of $500K in today's dollars.
Monthly savings: At 7% investment return, you need ~$1,874/month. Use the Goal Planner tab to see this automatically.
Example 2: Historical — 2000 to 2024
Scenario: $100,000 in 2000. What is its 2024 purchasing power?
CPI: 2000 = 172.2, 2024 = 310.3. Power = $100,000 ÷ (310.3/172.2) = $55,497. Almost half the purchasing power is gone — a 44.5% loss over 24 years.
Example 3: Real Wage Calculation
Scenario: You earn $75,000 and get a 3% raise. Inflation is 3.5%.
Real raise: (1.03 ÷ 1.035) − 1 = −0.48%. Despite a nominal raise, your real purchasing power fell by 0.48%. After 10 years of this, your real salary is $75,000 × (1.03/1.035)^10 = $71,500 in today's dollars.
US Inflation Rates by Era
| Period | Avg Annual Inflation | Cumulative | Context |
|---|---|---|---|
| 1970s | 7.1% | 97% | Oil crisis, OPEC embargo, stagflation |
| 1980s | 5.6% | 72% | Volcker rate hikes, gradual disinflation |
| 1990s | 3.0% | 34% | Great Moderation, tech productivity boom |
| 2000s | 2.6% | 29% | Dot-com bust, housing bubble, GFC |
| 2010s | 1.8% | 19% | Post-recession, ultra-low rate environment |
| 2020–2024 | 4.8% | 27% | Pandemic stimulus, supply chain crisis, 2022 peak at 8% |
Understanding Inflation and Your Money
The Silent Wealth Destroyer
Inflation is often called the "hidden tax" because it steadily erodes cash savings without any visible deduction. At just 3% annual inflation, $100 loses nearly half its purchasing power in 24 years. This calculator makes that invisible damage visible — and helps you build a strategy to fight back.
Category-Specific Erosion
General CPI averages mask significant variation. Education costs have averaged ~6% annually over 20 years, medical care ~4.7%, and housing ~4.1% — all substantially above the headline rate. If your spending is concentrated in these categories, your personal inflation rate is likely higher than reported CPI.
Protecting Your Purchasing Power
The break-even principle is simple: your investments must earn more than the inflation rate after taxes to preserve real wealth. High-yield savings accounts, Treasury Inflation-Protected Securities (TIPS), Series I Savings Bonds, real estate, and broad market equities have all historically outpaced inflation over long periods — though with varying risk profiles.
Planning in Today's Dollars
When setting retirement goals, always think in "today's dollars." A $1 million goal sounds substantial, but at 3.5% inflation over 25 years, you'd need $2.36 million to maintain the same purchasing power. The Goal Planner tab converts your real-dollar targets into the nominal savings you actually need to accumulate.