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How to Calculate What Money Will Really Be Worth Later
A number that does not change still loses value every year. Here is how to convert between nominal and real amounts, and why a savings rate below inflation means going backwards.
Inflation adjustment is compounding applied to prices instead of interest. To find what an amount will need to be in the future to buy the same things, multiply by (1 + inflation rate) for each year. To find what a past or future amount is worth in today's money, divide instead.
The two directions
These are the same relationship read from either end. The first tells you how much more you will need. The second tells you how much a headline figure is really worth once you strip out price rises.
Future amount needed = Today's amount x (1 + i)^n Value in today's money = Future amount / (1 + i)^n i = annual inflation rate as a decimal, n = number of years
Worked example: what a salary needs to become
You earn 48,000. Inflation runs at 3% a year. To keep the same purchasing power in five years you would need 48,000 x (1.03)^5 = 55,645.
If your pay instead rose to 52,000 over those five years, that looks like an 8.3% raise. In real terms it is a cut: 52,000 divided by (1.03)^5 is 44,857 in today's money, about 6.5% below where you started.
This is the calculation worth running before accepting that a pay rise is a pay rise. The test is whether the percentage increase beats cumulative inflation over the same period, not whether the number went up.
Worked example: cash sitting in a low-rate account
20,000 in an account paying 1.5%, with inflation at 3.5%, held for four years.
Nominal balance: 20,000 x (1.015)^4 = 21,228. The number went up.
Purchasing power: 21,228 / (1.035)^4 = 18,497 in today's money. You have roughly 1,500 less buying power than when you started, despite earning interest the whole time.
The balance rising is what makes this easy to miss. Nothing on a statement ever shows the loss.
The real rate of return
Using the example above: (1.015 / 1.035) - 1 = -0.0193, a real return of -1.93% a year. The quick subtraction gives -2%, close enough for most purposes.
The approximation drifts when rates are high. At 15% nominal and 10% inflation, subtraction suggests 5% but the exact figure is 4.55%. Below about 10% the shortcut is fine.
Real return = ((1 + nominal return) / (1 + inflation)) - 1 Rough approximation: Real return ≈ Nominal return - Inflation
How long different rates take to halve your money
The doubling shortcut works here too, in reverse: 72 divided by the inflation rate approximates how long until money is worth half as much. It is a useful reality check on any long-horizon plan, because the effect is slow enough to feel irrelevant year to year and large enough to reshape a decade.
| Annual inflation | Years to lose half of purchasing power | Value of 1,000 after 10 years |
|---|---|---|
| 2% | 35 years | 820 |
| 3% | 23 years | 744 |
| 5% | 14 years | 614 |
| 7% | 10 years | 508 |
| 10% | 7 years | 386 |
When this calculation is worth doing
It is least useful over short periods. Over one year at moderate inflation the adjustment is small enough that it rarely changes a decision. Over ten or twenty years it usually does.
- Assessing whether a pay rise or a rate increase is real or nominal.
- Setting a long-term savings target, where a fixed number will not mean the same thing by the time you reach it.
- Comparing a cost today with the same cost several years ago to see whether it actually rose faster than prices generally.
- Evaluating a fixed-income arrangement, where the payment stays constant while prices do not.
- Deciding how much cash to hold. Cash is safe in nominal terms and guaranteed to lose ground in real terms.
Common slips in inflation adjustments
- Adding inflation linearly across years. Ten years at 3% is not 30%; it is 34.4%, because it compounds.
- Mixing real and nominal figures in one comparison, such as an inflation-adjusted cost against an unadjusted salary.
- Assuming headline inflation matches your inflation. A published rate is an average across a basket that may look nothing like your spending.
- Projecting a single inflation rate decades ahead. Test a range instead, because the difference between 2% and 5% over 25 years is enormous.
- Forgetting that some costs move independently. Rent, tuition and healthcare frequently outpace the general rate.
Assumptions and limitations
The formula assumes a constant rate, which never holds in practice. Inflation arrives unevenly, and a period of high inflation followed by low inflation does not produce the same outcome as the average applied evenly, particularly if you were saving or drawing money during the spike.
It also assumes the published index reflects what you buy. Someone who rents in a city where rents are rising faster than the general index experiences higher personal inflation than the headline figure, and using the published rate understates the problem.
And it deliberately ignores everything else that affects your finances: tax, changes in income, and shifts in how you spend. An inflation adjustment answers one narrow question — what the same basket costs — which is why it is a useful input to a plan rather than a plan in itself. Where a number matters, run it at two or three different rates and look at the spread rather than trusting a single figure.
Separate nominal growth from purchasing power
An inflation adjustment answers a specific question: what amount at one date has the same purchasing-power relationship to another amount under the assumed inflation rate? It does not predict actual future prices. For planning, run the calculation at more than one plausible inflation rate when the time horizon is long, because small rate differences compound over many years.
Frequently asked questions
What inflation rate should I use for planning?
Many people use a long-run average of around 2-3% for stable economies, but the honest answer is to test a range. Running a plan at 2%, 4% and 6% shows how sensitive it is, which is more informative than a single assumption.
Does inflation affect debt?
Fixed-rate debt becomes easier to service in real terms as inflation rises, because the payment is fixed while incomes and prices are not. Variable-rate debt often does the opposite, since rates tend to rise in response to inflation.
What is the difference between nominal and real?
Nominal is the figure as stated. Real has been adjusted for inflation and is expressed in the purchasing power of a chosen year, usually today.
Is deflation just this in reverse?
Arithmetically, yes — use a negative rate. Economically it behaves quite differently, because falling prices tend to come with falling wages and rising real debt burdens.
Does inflation reduce the value of cash?
If prices rise while the cash amount stays unchanged, that cash generally buys fewer goods and services. The calculation estimates the change using the inflation rate you assume.
Is an inflation-adjusted value a guaranteed future amount?
No. It is a model based on an assumed inflation rate. Actual inflation can vary across time and across categories of goods and services.
Conclusion
Inflation adjustment is the same compound formula as interest, applied to prices, and used in whichever direction the question needs. The habit worth building is comparing like with like: when you see a figure that has gone up, check whether it went up faster than prices did. That single check is what separates a real increase from a number that merely got bigger, and it applies to salaries, savings rates and long-term targets alike.
Figures in this article are illustrative. Results depend on your own rates, fees, taxes and circumstances, and are for educational and planning purposes rather than financial advice.