The number in the account never falls. What it buys does — quietly, and without anything visibly happening.
Inflation is not a number on the news. It is the reason the same weekly shop costs more than it used to, and the reason money left alone gets quietly smaller without anything visibly happening to it.
Inflation is the rate at which the general price level rises. The UK's headline measure is CPI — the Consumer Prices Index — which tracks the cost of a representative basket of goods and services and reports how much more that basket costs than a year earlier.
CPI at 3% means the basket costs 3% more than last year. It does not mean everything rose 3%. Some things rose far more, some fell, and the index is an average weighted by what households actually buy.
You will also see CPIH, which includes owner-occupiers' housing costs, and RPI, an older measure that runs higher and is being phased out but still appears in some rail fares, student loans and index-linked gilts.
The Bank of England targets 2% inflation. At that rate, prices roughly double every 36 years. That sounds slow until you apply it to a cash balance.
The number in the account never falls. What it buys does. At 4% inflation, £10,000 held as cash for twenty years still says £10,000 — but it buys what £4,560 buys today.
A savings account paying 4% while inflation runs at 3% is not paying you 4%. It is paying you roughly 1% in real terms — the return after inflation.
The rough version: real return ≈ nominal return − inflation.
This reframes what "safe" means. Cash cannot fall in nominal terms, which is exactly why it is right for money you need soon. But over long periods, cash has frequently delivered a negative real return, which makes it a poor home for money you will not touch for twenty years. Both statements are true at once, and the deciding factor is your time horizon.
Over one year, the stock market is far riskier than cash — it can easily fall 20% or more.
Over thirty years, the risk profile inverts. The dominant risk to a thirty-year cash balance is not a crash; it is the certainty of erosion. The dominant risk to a thirty-year investment is a poor sequence of returns, which history suggests has been the smaller of the two dangers over long horizons.
No guarantees exist here, but broadly:
Equities. Companies can raise their own prices, so revenues and eventually dividends tend to move with inflation over long periods. Volatile in the short run.
Index-linked gilts. Explicitly linked to RPI, though their market prices still move with interest rates.
Property. Rents and values have historically tracked inflation over long stretches, with high transaction costs and no liquidity.
Cash at a competitive rate. Keeps pace when the rate exceeds inflation, which is exactly when savings rates are worth actively chasing.
You cannot control inflation. You can control four things.
The rate on your cash. The gap between a high-street easy-access account and the best available rate is often more than a percentage point, on money that is doing nothing else. Our savings account comparison shows what is currently available.
Your tax on returns. Inflation erodes the gross return; tax erodes what is left. An ISA removes the second one entirely.
Your costs. Fees come out of a return that inflation has already reduced.
Your horizon. The single largest lever. Money with a longer runway can be invested rather than held.
If you are saving towards something specific and want the target to keep pace, the savings goal and sinking funds tracker makes the monthly number explicit.
For the mechanics of why long horizons behave so differently, see how compound interest works.