Number Inflation Calculator
Inflation is compound interest running against you. Enter any amount, a rate and a span of years, and see both directions at once: what today’s price becomes, and what a future sum shrinks to in today’s money.
How it works
Both directions are one formula: future value = amount × (1 + rate)years, and today’s-money value = amount ÷ (1 + rate)years. The purchasing-power line is the quiet one: at 3% inflation, money halves in buying power about every 24 years — the mirror image of the rule of 72.
Formula & worked example
Formula: Future value = amount × (1 + rate)years; today’s-money value = amount ÷ (1 + rate)years — one formula read in both directions. Purchasing power halves every ln(2) ÷ ln(1 + rate) years — about 23.4 years at 3%.
Worked example: At 3% inflation for 10 years, a $100 price becomes $134.39 — and $100 received in ten years buys only what $74.41 buys today, a 25.6% loss of purchasing power without a single dollar leaving the account.
When to use this
- You know what rent, groceries or insurance cost today and want a plausible future cost if inflation holds at a given rate.
- You have a retirement or savings target in future dollars and need it translated back into today's money before you judge it.
- Cash is sitting in a non-interest account for years and you want the real cost of leaving it there.
- A flat salary, a fixed pension or a long fixed-price contract needs testing against rising prices.
How to use it, step by step
- Enter the amount — a price today, or a sum you expect to receive later.
- Set an inflation rate; run the long-run average first, not the scariest headline.
- Set the years honestly — inflation's damage is mostly a long-horizon story.
- Read both directions: the future cost of today's amount, and today's-money value of that same amount received later.
- Re-run at a rate one or two points higher as a stress test; the gap between the two runs is your planning margin.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Amount | The sum whose buying power you are tracking | Anything from a $100 bill to a retirement pot |
| Inflation rate | Assumed yearly rise in prices | Long-run US average near 3%; personal baskets vary |
| Years | The span inflation compounds over | 5 years for a car fund; 20–30 for retirement |
Another worked example
Take $1,000 at 4% inflation for 20 years: the same basket of goods costs $2,191.12, a $1,191.12 increase. Read it the other way and $1,000 arriving 20 years from now buys only $456.39 worth of today's goods — a 54.36% loss of purchasing power — and at 4% buying power halves every 17.67 years.
Frequently asked questions
What does $100 become after 10 years at 3% inflation?
A price of $134.39 — and the flip side matters more: $100 received in ten years buys only what $74.41 buys today. Same formula, two directions, one uncomfortable lesson.
How long until money loses half its value?
Divide 72 by the inflation rate: at 3%, about 24 years; at 5%, about 14 years; at 7%, about a decade. Cash under the mattress is on a clock.
What inflation rate should I plan with?
Long-run US CPI averages near 3%, and most retirement planning uses 2.5–3.5%. Run your plan at 4% too — if it only works at exactly 2%, it does not work.
Is a 5% CD yield a 5% return?
Nominally yes, really no: subtract inflation. At 5% APY and 3% inflation your purchasing power grows about 2% a year — the CD Calculator shows the nominal figure, this tool shows what it will buy.
💿 Earning interest against it?
The CD Calculator works out exactly what a deposit grows to — then bring that number back here to see what it will buy.
Does inflation compound, or is it just the rate times the number of years?
It compounds. Each year's price rise applies to a price level that has already risen, exactly like interest in reverse. That is why the simple multiplication understates long spans so badly: the gap between the two methods is small over two or three years and enormous over twenty.
Why does my personal inflation feel higher than the official rate?
Because CPI is an average basket and yours is not. If most of your spending goes to rent, childcare, healthcare or groceries in a year when those run hot, your personal rate can sit well above the headline figure — and the reverse when your big costs are flat. For planning your own future costs, a rate based on your actual basket is the more honest input.