Why Money Can Be Worth Less in the Future
If you have £10,000 today and still have £10,000 in ten years, the number shown on your balance has not changed. But that does not necessarily mean the money has kept the same value to you.
The reason is purchasing power — the amount of goods and services your money can buy. When prices rise over time, the same £10,000 may pay for less than it does today. You still have £10,000 in pounds, but its purchasing power has fallen.
For example, imagine something costs £100 today. If its price eventually rises to £125, having the original £100 would no longer be enough to buy it. Nothing has been taken from your £100; the price of what you want to buy has increased.
This distinction between the amount of money and what that money can buy is central to understanding what money may be worth in the future.
Calfiny’s Inflation Calculator lets you explore how different inflation rates and time periods can affect the purchasing power of an amount over time.
If you want to understand the underlying concept in more detail, Why Inflation Reduces Your Purchasing Power explains how rising prices can affect the real value of money.
How Inflation Changes the Value of Money Over Time
Inflation does not usually reduce purchasing power in one sudden step. Its effect can build over time as prices continue to change.
This means the length of time involved can make a substantial difference.
Consider £10,000 and assume inflation averages 3% a year. The £10,000 itself does not disappear or become a smaller number. Instead, its purchasing power gradually declines as the general level of prices rises.
This illustration shows the purchasing power of £10,000 after different periods if inflation averaged 3% a year. At 3% average annual inflation, £10,000 would still be £10,000 in nominal terms after 30 years, but its purchasing power would be equivalent to roughly £4,120 in today’s money. Illustrative only. This assumes a constant 3% annual inflation rate. Actual inflation changes over time, so this is not a prediction of future purchasing power.What £10,000 Could Be Worth in Today's Money
The effect becomes increasingly noticeable as the period gets longer. After five years, the difference in purchasing power is relatively modest. After 20 or 30 years, the same £10,000 represents considerably less spending power under the same assumption.
This happens because the effect of inflation is cumulative. Each year’s price increase builds on the price level already reached rather than inflation simply removing the same fixed amount of purchasing power every year.
Both the inflation rate and the length of time therefore matter when estimating what a future amount of money might represent in today’s terms.
How Do You Calculate What Future Money Is Worth Today?
To estimate what a future amount of money would be worth in today’s terms, you need three main pieces of information:
the future amount, the assumed inflation rate and the number of years.
The calculation works backwards from the future amount. Rather than increasing today’s money to reflect higher future prices, it removes the cumulative effect of the assumed inflation to estimate the equivalent purchasing power in today’s money.
Suppose you expect to have £50,000 in 20 years and want to estimate what that amount could be worth in today’s purchasing power if inflation averaged 2.5% a year. Under these assumptions, £50,000 received in 20 years would have purchasing power broadly equivalent to about £30,514 today. You would still have £50,000, but higher prices would mean it could buy less than £50,000 can buy now. Illustrative only. This assumes inflation remains at 2.5% every year for 20 years. Actual inflation changes over time.
What Could £50,000 in 20 Years Be Worth Today?
The important part of the calculation is the cumulative effect.
With 2.5% annual inflation, you cannot simply multiply 2.5% by 20 and treat the result as the complete change in purchasing power. Each year’s change occurs on top of the price level reached in the previous year.
This is why a relatively modest annual inflation assumption can produce a much larger difference when the period extends over several decades.
The £30,514 result should not be interpreted as a prediction of what £50,000 will actually be worth in 20 years. It answers a narrower question:
If inflation averaged 2.5% over that period, what would £50,000 of future spending power be approximately equivalent to today?
Why the Inflation Rate Makes Such a Difference
Time is only one part of the calculation. The inflation rate itself can also make a substantial difference.
Suppose you expect to have £100,000 in 20 years. The amount and time period remain unchanged in each example below. Only the assumed average rate of inflation changes.
See how changing the assumed average inflation rate changes the purchasing power of the same £100,000 future amount. A difference of only a few percentage points in average annual inflation can produce a much larger difference in purchasing power when it continues over a long period. Illustrative only. These examples assume a constant inflation rate throughout the full 20 years. Actual inflation changes over time and these figures are not predictions of future purchasing power.What Could £100,000 in 20 Years Be Worth Today?
2% inflation
3% inflation
4% inflation
The comparison demonstrates why the inflation assumption matters so much over longer periods.
At an assumed 2% average inflation rate, £100,000 in 20 years is equivalent to approximately £67,297 in today’s purchasing power. Increasing the assumption to 4% reduces the equivalent figure to approximately £45,639.
That does not tell us which outcome will occur. Instead, it shows how sensitive the result is to the inflation assumption being used.
Testing more than one rate can therefore provide a broader view than relying on a single long-term inflation scenario.
Future Value and Purchasing Power Are Not the Same Thing
When thinking about money many years from now, future value and purchasing power can both be useful concepts, but they answer different questions.
Future Value
Future value looks forward. It estimates what an amount of money could grow to over time using an assumed rate of interest, return or growth. It tells you how many pounds you could have under those assumptions.
Purchasing Power
Purchasing power considers what a future amount of money could be equivalent to after allowing for rising prices. It helps put those future pounds into today’s terms.
Future value tells you how many pounds you could have. Purchasing power helps you understand what those future pounds could be able to buy relative to today.
Suppose £50,000 grows to £80,000 over a long period. The future value is £80,000, but that does not necessarily mean purchasing power has increased by £30,000.
Prices may also have risen while the money was growing.
If the money grows more quickly than prices rise, its purchasing power may increase. If prices rise more quickly than the money grows, its purchasing power may fall despite the balance containing more pounds.
Calfiny’s Future Value Calculator lets you explore how an amount could grow over time using different assumptions. The Inflation Calculator approaches the question from the other direction by showing what a future amount could represent in purchasing-power terms.
The same distinction is important when investment returns are discussed in nominal and real terms. Nominal vs Real Returns explains how inflation can change the interpretation of an investment return.
Why Purchasing Power Matters for Long-Term Goals
Purchasing power becomes particularly relevant when a financial goal is many years away.
Suppose you decide today that £100,000 represents the amount associated with a long-term goal. If the money will not be needed for another 20 or 30 years, reaching a balance of £100,000 at that future date does not necessarily provide the purchasing power that £100,000 has today.
Prices may have risen considerably during the intervening period.
This does not mean you can calculate today exactly how much a future goal will cost. Future inflation is uncertain, and the price of a particular product, service or goal will not necessarily move at exactly the same rate as general inflation.
Different costs can change at different rates.
The useful principle is therefore broader: when a financial target is many years away, the number of pounds involved and the purchasing power those pounds may eventually provide are two different considerations.
This is one reason inflation becomes increasingly relevant when thinking about longer-term financial goals.
Inflation Assumptions Are Not Predictions
Any calculation of future purchasing power requires an assumption about inflation.
That assumption allows you to explore a possible scenario. It does not tell you what inflation will actually be.
For example, entering an annual inflation rate of 3% answers the question:
What could happen to this money’s purchasing power if inflation averaged 3% over the period?
It does not mean inflation is expected to remain at exactly 3% each year or even that it will average 3% across the full period.
Actual inflation changes over time. Some periods experience relatively low inflation, others higher inflation, and prices can occasionally fall.
The further into the future a calculation extends, the more uncertainty surrounds the assumptions being used.
This is why testing several assumptions can be useful. Comparing results at 2%, 3% and 4%, for example, cannot tell you which rate will occur, but it can show how different inflation scenarios affect the same amount of money.
Inflation calculations are therefore best understood as planning scenarios rather than forecasts.
Calculate What Your Money Could Be Worth
The Inflation Calculator lets you enter an amount, choose a timeframe and test different inflation assumptions to see how the purchasing power of that money could change.
Rather than relying on one result, you can run the calculation several times while keeping the amount and timeframe unchanged and varying the inflation rate. This can help show how sensitive a longer-term amount is to different assumptions.
The results remain illustrations rather than predictions of future inflation or the exact cost of a particular financial goal.
Used in that way, the calculator can help answer the central question behind this guide:
If I have a certain amount of money in the future, what might that amount be worth in today’s purchasing power?
Conclusion
The number of pounds you have and the amount those pounds can buy are not necessarily the same thing.
If prices rise over time, a future amount of money can have less purchasing power even though its nominal value has not fallen. The longer the period and the higher the average rate of inflation, the greater that effect can become.
This is why future value and purchasing power should be kept separate. A balance may grow in pounds while some of that apparent growth is offset by higher prices.
Calculations can help put this effect into context, but their results depend on the inflation rate and timeframe assumed. They are most useful for exploring what could happen under different scenarios, rather than predicting exactly what money will be worth many years from now.
