Quick Summary
A guide to understanding inflation calculations - how purchasing power erodes over time, the formula behind it, and why it matters for financial planning.
In 1990, the median US home price was about $79,000. In 2024, it was roughly $420,000. A five-fold increase sounds dramatic - and it partly is - but inflation alone accounts for a significant chunk. That $79,000 in 1990 dollars is equivalent to about $190,000 in 2024 dollars. The rest of the increase is real appreciation, not just the dollar losing value.
Separating real changes from inflation noise is one of the most useful financial skills. And it starts with a simple formula.
The Inflation Calculator shows how purchasing power shifts over any time period. No signup required.
The Two Directions
Inflation calculations go two ways, and both are useful.
Forward: What will today’s money buy in the future? At 3% annual inflation, $100 today has the purchasing power of about $74 in ten years. Your savings account might show $100, but it buys what $74 used to.
Backward: What would past money be worth now? $100 in 2000 had the same purchasing power as roughly $183 today. When someone says they earned $40,000 in 1995, that is about $82,000 in current dollars.
The formula for both:
Future cost = Present value x (1 + inflation rate)^years
Present purchasing power = Future value / (1 + inflation rate)^years
The Slow Erosion
A table makes the scale of this clearer. Here is what happens to $100 of purchasing power at different rates:
| Years | 2% Inflation | 3% Inflation | 4% Inflation |
|---|---|---|---|
| 5 | $90.57 | $86.26 | $82.19 |
| 10 | $82.03 | $74.41 | $67.56 |
| 20 | $67.30 | $55.37 | $45.64 |
| 30 | $55.21 | $41.20 | $30.83 |
At 3%, money loses nearly half its purchasing power in twenty years. This is the number that makes retirement planning so different from short-term budgeting. A $50,000 annual budget today requires about $90,000 in twenty years and $121,000 in thirty years to buy the same things. Not more things - the same things.
Your Inflation Is Not the National Average
The Consumer Price Index measures a weighted basket of goods. But nobody buys the basket. Individual spending patterns create a personal inflation rate that can differ meaningfully from the headline number.
Categories that inflate faster than average: Healthcare (historically 5-6% per year), education and tuition (5-8%), housing in high-demand cities, childcare.
Categories that inflate slower or deflate: Electronics and technology (prices generally fall), clothing, many consumer goods.
Someone spending 30% of their budget on healthcare - common for retirees - faces a personal inflation rate well above 3%. Someone whose major expenses are groceries and electronics might experience closer to 2%. The national average is useful as a starting point, but personal spending patterns tell the more accurate story.
Nominal vs. Real: The Most Misunderstood Distinction
When someone says the stock market returns “7%,” they usually mean the inflation-adjusted (real) return. The nominal return - what the account statement shows - has historically averaged closer to 10%. The difference is inflation eating into the gains.
This matters for any long-term projection:
Nominal return: What the account shows you gained. Real return: What that gain actually means in purchasing power.
A portfolio returning 8% in a year with 3% inflation has a real return of about 5%. The balance grew 8%, but only 5% of that represents increased buying power. The other 3% just kept pace with rising prices.
For long-term financial planning, using real returns produces more honest projections. The numbers are smaller but more meaningful.
Inflation and Fixed Debts: A Silver Lining
Here is a counterintuitive angle: inflation helps borrowers with fixed-rate debt.
A $2,000 monthly mortgage payment is $2,000 today. If incomes rise with inflation (say 3% annually), that same $2,000 payment feels more like $1,500 in ten years, relative to income. The debt amount stays fixed while the dollars used to pay it become less valuable.
This is one reason low-rate, fixed-rate mortgages are often kept rather than paid off aggressively. If the mortgage rate is below the inflation rate, the debt is effectively shrinking in real terms. Variable-rate debt does not have this benefit since rates can adjust upward.
Salary, Raises, and the Illusion of Progress
A 3% annual raise with 3% inflation means zero real increase. The paycheck is bigger but buys the same amount. Only raises above the inflation rate represent genuine gains in buying power.
This reframes how to think about career moves. A job paying $80,000 in a city with 2% local inflation might provide more actual purchasing power than $95,000 in a city where housing costs are rising 6% a year. The nominal salary is misleading without the inflation context.
Building Inflation Into Plans
Any financial plan extending beyond five years needs an inflation assumption. A few practical approaches:
Use real return rates for investment projections. Instead of projecting 10% stock returns, use 7%. The results are smaller but more honest about future purchasing power.
Increase savings contributions annually. If you save $500/month this year, $515/month next year (a 3% bump) keeps the real savings rate constant as prices and presumably income rise.
Review recurring expenses yearly. Insurance premiums, property taxes, subscriptions, and healthcare costs tend to creep up. Budgeting for these increases prevents the slow squeeze of expenses growing faster than the budget allocated to them.
The Financial Planning Template helps model projections with inflation assumptions. The Retirement Financial Planning Template specifically factors inflation into long-term retirement projections, where the impact is largest.
More on Growth & Purchasing Power
- Compound Interest: The Math Behind Growth - How compounding works and why it matters for outpacing inflation
- Savings Calculator: How Your Money Grows - Model how regular contributions grow over time