Inflation purchasing-power calculator: what will this money be worth

Inflation does not take your money in one go; it shaves a little off every year. The two small tools below use the plainest formulas: one works out how much purchasing power cash keeps after a few years of sitting still, the other shows whether your return actually beats inflation. Change the numbers and the answer changes with them, so put in your own.

How the loss of purchasing power is calculated

The first tool uses one line of arithmetic:

Purchasing power after N years = amount ÷ (1 + annual inflation)^years

The loss is simply one minus that result as a share of the original amount. With the defaults of 100,000 at 3% over 10 years: 100,000 ÷ 1.03¹⁰ is about 74,409, leaving roughly 74.4% of the purchasing power and a cumulative loss of 25.6%.

There is a common way to get this wrong that deserves its own line: do not use amount × (1 − inflation)^years. On the same figures that gives 100,000 × 0.97¹⁰, about 73,742, some six hundred short of the right answer. The difference is that inflation means prices going up, not your money being cut by 3% a year. You divide the money by the risen prices rather than shrinking the money itself. At small numbers the two are close; over many years or at higher inflation the gap becomes obvious.

Working backwards is a different job

This tool runs forwards: you supply an inflation assumption and it projects ahead. If your question is the reverse, such as what 10,000 from twenty years ago is worth today, a single fixed inflation rate will not do, because inflation varied a great deal from year to year and an average smooths away exactly what you need.

The right method uses the official consumer price index directly:

Value today = original amount × (this year's CPI ÷ that year's CPI)

Both index values have to come from the same official series. National statistics offices and central banks publish CPI figures year by year; look up the two years you need and substitute them. This site does not carry historical price data, and it is not worth assembling from figures quoted second-hand, since different series are built on different baskets and will not agree.

Which inflation rate to enter

The published national rate is a sensible starting point, but it measures a fixed basket for an average household and may not resemble yours. If rent, education or healthcare take a large share of your spending, your felt rate usually runs above the official one, and the loss shown here will look milder than what you experience.

A sturdier habit is to work in a range rather than a single point: enter a figure you consider low, then one you consider high, and look at the distance between the two results. If even the optimistic case makes you uncomfortable, the conclusion is already clear. If only the pessimistic case calls for action, there may be no hurry.

The longer the period, the less a fixed rate can be trusted. Beyond ten years, treat the output as an order of magnitude rather than a precise figure.

How the two tools fit together

They answer two neighbouring questions:

• The first tells you the scale of the loss from doing nothing.
• The second tells you whether what you are currently earning is enough to hold that off.

They are most useful in sequence: see the cost of leaving money still, then check whether the thing you are actually doing with it (a current account, a term deposit, any product with a nominal return) is genuinely ahead. If the second tool returns a negative number, your present arrangement is slowing the erosion rather than stopping it. Whether that is worth changing is a separate decision, and not one these two figures can make for you.

Neither tool includes taxes or fees, and both assume a fixed inflation rate. In practice both of those move.

FAQ

How do you calculate the value of money with inflation?

Purchasing power after N years = amount divided by (1 + annual inflation) raised to the number of years. Taking 100,000 at 3% inflation over ten years, 100,000 divided by 1.03 to the tenth power is about 74,409, meaning roughly 74.4% of the purchasing power remains and 25.6% has been lost.

Why can't I multiply the amount by (1 minus inflation)?

Because inflation means prices rising, not your money being cut by a slice each year. The correct step is to divide the amount by the risen prices. On the same figures of 100,000 at 3% over ten years, the multiplication gives about 73,742 against the correct 74,409, some six hundred short. The longer the period and the higher the inflation, the larger that error becomes.

How do I work out what money from a past year is worth today?

Do not project backwards with a single fixed rate, because year-to-year inflation varied widely. Use the official consumer price index instead: value today = original amount × (this year's CPI ÷ that year's CPI). Both figures must come from the same official series, as indices built on different baskets cannot be mixed.

Should I enter the official inflation rate?

It works as a starting point, but the official figure measures a fixed basket for an average household. If rent, education or healthcare take a large share of your spending, your felt rate runs higher and the loss shown will look milder than your experience. Run it once low and once high to see the range, and over longer periods treat the result as an order of magnitude.

Once you have the numbers, read on

The numbers are only a starting point. The real question is: given that cash is shrinking, where to put some of it and how much. Read these in order to think it through.

• Why cash loses value: first understand exactly how inflation eats purchasing power.
• Safe-haven assets compared: the trade-offs of gold, silver, dollars, short-term bonds and bitcoin.
• How much to allocate: more is not better; decide the share first.
• Pre-buy checklist: before you actually act, check each item to dodge the common traps.

HoldValue is an independent education site. It explains how safe-haven assets work and where the risks are, so you can judge for yourself before acting. We never operate accounts for anyone and never collect sensitive information.

• hold@holdvaluehq.com