How Inflation Is Calculated
Inflation compounds. A 3% rise each year is not 30% over ten years — it is 34.4%, because each year’s increase applies to a price that already rose the year before. This is the same compounding maths that drives investment growth, working against you instead of for you.
Formula
Real value = Amount ÷ (1 + rate)years
Those two lines answer different questions, and mixing them up is the most common mistake people make. Future cost tells you how many dollars you will need later to buy what your money buys now. Real value tells you what a fixed sum — a pension payment, cash under the mattress — will actually be worth once prices have risen around it.
A Worked Example
Suppose you have $50,000 in a savings account paying no interest, and inflation runs at 3% for 15 years.
Step 1 — the compounding factor
1.0315 = 1.5580. Prices end up roughly 56% higher than they started.
Step 2 — what you would need
$50,000 × 1.5580 = $77,898. That is what it would take in 15 years to buy what $50,000 buys today.
Step 3 — what your money is actually worth
$50,000 ÷ 1.5580 = $32,092 in today’s money. The account still says $50,000, but it buys about 36% less. Nothing was withdrawn — the loss is entirely from prices rising elsewhere.
Why This Matters for Savings
The number that matters on a savings account is not the interest rate, it is the real return — interest minus inflation. An account paying 2% while inflation runs at 3% loses about 1% of purchasing power every year, even though the balance is going up. Savers often read a rising balance as progress when the money is quietly getting smaller.
This is also why long-horizon plans need inflation built in. A retirement target of $1,000,000 set thirty years out is not a target of $1,000,000 in today’s terms — at 3% it is closer to $412,000 of present-day spending power. Use the compound interest calculator to project growth, then run the result through this tool to see what it will be worth when you get there.