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Inflation Calculator: Future Cost and Purchasing Power
Pick a question: what an item will cost after years of rising prices, what an amount of money will still buy, or what yearly inflation rate links a past price to a later one.
The three formulas behind the tool
Inflation is the rise in the general price level, so one unit of money buys less over time. Because each year's rise applies to prices that already rose, the arithmetic compounds. Three closely related formulas cover almost every question about it:
- Future cost:
cost = P × (1 + i)t, wherePis today's price,ithe yearly inflation rate as a decimal andtthe years. - Purchasing power:
value = M ÷ (1 + i)t, whereMis an amount you will receive aftertyears. It tells you how much of today's shopping that amount represents. - Implied rate:
i = (later price ÷ earlier price)1/t − 1. Use it when you know two prices and the gap in years but not the rate.
The second formula is the inverse of the first. If prices double, money is worth half as much in terms of goods.
How quickly prices compound
Small yearly rates become large changes over long periods. This table shows what an item priced at 100 would cost later, using the first formula.
| Yearly inflation | After 10 years | After 20 years |
|---|---|---|
| 2% | 121.90 | 148.59 |
| 3% | 134.39 | 180.61 |
| 5% | 162.89 | 265.33 |
At 3% a year, prices rise by roughly four fifths in two decades, so a sum that looks comfortable today may cover far less later. The same logic shows why cash held at an interest rate below inflation slowly loses real value even though the number in the account rises.
Reading the three answers
The first mode suits budgeting: tuition, rent, a future purchase or a long-term contract. The second mode suits comparing money across time, such as a pension payment, a legacy or a fixed salary. Express a future sum in today's terms and the comparison with current prices becomes fair. The third mode suits history: enter the price of a basket or service in two different years and see the average yearly rate.
The implied rate is an average. If prices rose slowly for years and then jumped, the single compounded figure describes neither period well. The table of simple (non-compounded) change is shown only as a sanity check, since compounding is the correct way to average price growth.
Common mistakes and limits
- Using one rate for everything. Official consumer price indices measure an average basket. Your own costs, such as education, healthcare, food or energy, may rise faster or slower than that average.
- Mixing real and nominal numbers. A savings rate quoted before inflation is a nominal rate. Subtract inflation, or divide as shown above, to see the real result.
- Assuming the rate stays fixed. Real inflation changes from year to year and can briefly turn negative. Test a low case and a high case.
- Forgetting the period. Use years, not months, or convert months by dividing by twelve.
This calculator is for learning and planning. It does not forecast prices and it does not use official price data; enter the rate you want to test.
Worked example
A household item costs 250 today. What might it cost in 15 years if prices rise 4% a year?
Inputs
| What do you want to find? | Future cost of something that costs this much today |
|---|---|
| Amount or earlier price | 250 |
| Assumed yearly inflation | 4 % |
| Number of years | 15 |
Result
Something that costs 250.00 today, after 15.00 years at 4% a year.
| Increase in price | 200.24 |
|---|---|
| Price level multiplier | 1.8009 |
| Change in value | 80.09% |
Year by year
| Year | Price |
|---|---|
| Year 1 | 260.00 |
| Year 2 | 270.40 |
| Year 3 | 281.22 |
| Year 4 | 292.46 |
| Year 5 | 304.16 |
| Year 6 | 316.33 |
| Year 7 | 328.98 |
| Year 8 | 342.14 |
| Year 9 | 355.83 |
| Year 10 | 370.06 |
| Year 11 | 384.86 |
| Year 12 | 400.26 |
- Formula: future cost = amount × (1 + rate)^years. The rate is assumed constant.
Financial disclaimer: Results are estimates for planning and education. They are not financial, tax or legal advice. Fees, taxes, rates and rules vary by lender, product and country, so confirm figures with your provider or a qualified adviser before making decisions.
Frequently asked questions
How do I calculate the future cost of something with inflation?
Multiply today's price by one plus the yearly inflation rate raised to the number of years. At 3% for 10 years the multiplier is about 1.344.
What does purchasing power mean?
Purchasing power is the quantity of goods and services a given amount of money can buy. When prices rise, the same amount buys less, so its purchasing power falls.
How do I find the inflation rate between two prices?
Divide the later price by the earlier price, raise the result to the power of one over the number of years, and subtract one. The calculator's third mode does this for you.
Can I enter negative inflation?
Yes. A negative rate models deflation, where prices fall. The future cost then becomes smaller than today's price.
Which inflation rate should I use for planning?
National statistics offices publish consumer price indices, and central banks often state a target. Pick a rate that suits your own spending, and test a higher one too.
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References and sources
- U.S. Bureau of Labor Statistics: Consumer Price Index program, an example of an official price-index publisher. Link
- Standard time-value-of-money texts: compounding of a constant growth rate.