The cost of leaving money standing still
This calculator isolates a specific, easy-to-overlook cost: what happens to a fixed sum of money's real buying power if it earns no return at all while prices around it keep rising. It's a deliberately stripped-back companion to our general inflation calculator, framed specifically around a savings balance sitting idle, to show the erosion in pounds and as a percentage of the original amount.
Why this scenario is more common than it sounds
Money left in a non-interest or very low-interest current account, cash kept at home, or a savings account with a rate that's fallen behind since you opened it, can all experience close to this exact scenario in practice. It's also relevant to money temporarily parked while you decide what to do with it — an inheritance, redundancy payment, or house sale proceeds sitting in a low-rate account while you consider your options are quietly losing real value the longer that decision takes.
How much of a difference even a modest interest rate makes
Comparing this calculator's result against our savings calculator for the same amount and term is instructive: even a relatively modest interest rate meaningfully offsets the erosion shown here, and a rate at or above the assumed inflation rate protects your real purchasing power entirely, at least on the numbers if not with certainty about future inflation. This is the core argument against leaving substantial sums sitting in a poorly-paying account indefinitely, particularly once an emergency fund is already in place.
Erosion over different time horizons
The effect shown here compounds with time in the same way growth does, just working against you rather than for you — the proportion of value eroded over 20 years at a given inflation rate is considerably more than double the erosion over 10 years at the same rate, not simply twice as much. This is worth bearing in mind for money you know you won't need for many years; the case for finding it a better home than a stagnant account only strengthens the longer the likely holding period.
What this doesn't capture
This calculator doesn't account for tax on any interest that might otherwise have been earned, or for the psychological and practical value of having cash instantly accessible in an emergency, which is a genuine benefit that shouldn't be dismissed purely on inflation-erosion grounds. It's one input into a broader decision about where to hold money, not a complete verdict on the right home for every pound — our savings versus investment calculator and emergency fund guide can help with the wider picture.
A worked example
Take £20,000 left sitting in a non-interest current account for 10 years, with inflation running at the calculator's default assumption of 2.5% a year. Its remaining purchasing power in today's terms falls to roughly £15,600 — a loss of around £4,400, or about 22% of the original value, even though the account statement would still show exactly £20,000 throughout.
Extend the same scenario to 20 years instead of 10, and the erosion accelerates: purchasing power falls to approximately £12,200, a loss of roughly £7,800, or about 39% of the original value — nearly double the proportional loss of the 10-year scenario, despite the time period only doubling. That non-linear acceleration is exactly why leaving a substantial sum in a stagnant account becomes progressively costlier the longer it's left there.
A practical next step
If this result shows a meaningful loss of purchasing power on money you don't need at short notice, the practical next step is usually to compare the account it's currently sitting in against better-paying alternatives, or to consider whether some of it could reasonably be invested instead for a longer-term goal. Neither move eliminates risk entirely — a better savings rate can still fall behind inflation, and investing introduces the possibility of the balance falling in value — but leaving a large sum indefinitely in an account that's demonstrably losing real value each year is rarely a deliberate choice once the numbers are actually seen laid out like this.
Frequently asked questions
Does this apply to money in a pension too?
The same underlying maths applies to any static amount, but pension and investment balances are rarely static — they're usually invested and aiming for growth, so this calculator is most directly relevant to cash specifically, not to invested balances.
What inflation rate should I use for a long-term projection?
A commonly used starting point is the Bank of England's 2% target, though it's sensible to also test a higher assumption to see a more cautious outcome, since actual inflation has exceeded that target for extended periods in the past.
Is any erosion normal, or should I always try to beat inflation exactly?
Some erosion on genuinely short-term cash (an emergency fund, money needed within the next year or two) is a reasonable trade-off for safety and accessibility — the concern is mainly with larger sums held for years with no plan to move them somewhere better.
Can I use this to check a specific historical period rather than a future projection?
Yes — enter a historical amount and the actual inflation rate over a past period you're interested in, and the calculator will show the equivalent purchasing power loss over that specific timeframe just as readily as a forward-looking projection.
Is there a way to protect cash savings from this kind of erosion entirely?
Not completely, since even the most competitive savings rate offers no absolute guarantee of beating future inflation — the closest practical protection is comparing rates regularly and, for longer horizons, weighing whether some of the money would be better suited to investing instead. Revisiting this figure whenever your circumstances or the wider inflation outlook shift meaningfully keeps the comparison useful rather than stale.
Does this calculator work for a foreign currency amount too?
The maths is identical for any currency, though you'd need an inflation rate relevant to that currency's own economy rather than the UK figure, since inflation rates can differ considerably between countries at any given time.
Is it worth reviewing this figure alongside a pay rise negotiation?
It can be — comparing how your income has moved against how prices have moved over the same period gives a more grounded sense of whether your real spending power has actually improved, stayed flat, or fallen, beyond just looking at the headline salary figure.