Hundred SummersPremium Bonds calculator: the prize rate against a savings account, after your tax
Expected tax-free prizes on your holding at the prize fund rate, against the interest a savings account would leave you after tax at your band and personal savings allowance, and the gross rate an account would need to match. Your figures never leave your browser.
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Worked example
Computed when this page was built by the same engine that runs the calculator above, so the figures below and the live tool can never disagree. Change any input above to see your own.
| Inputs | |
|---|---|
| Holding | £20,000 |
| Prize fund rate | 4.35% |
| Best savings rate | 4.5% |
| Other income | £45,000 (basic-rate taxpayer) |
| Results | |
|---|---|
| Expected prizes a year (tax-free) | £870 |
| Savings interest after tax | £900 (tax £0) |
| The savings account pays more by | £30 |
| Gross savings rate that would match the prize rate | 4.35% |
The next question
How big should my cash cushion be? →Emergency fund calculator
Or answer it with everything else: the full Hundred Summers plan connects your pay, pensions, savings, property, tax and spending year by year, and stress-tests them across 500 simulated market histories.
Read the guide
- Premium Bonds, cash and tax: where the money you might need should sit →The personal savings allowance and why higher-rate savers cross it at ordinary balances, the after-tax comparison that decides Premium Bonds against a savings account, cash ISAs, and what inflation does to money that sits still.
The comparison that matters is after tax
Premium Bond prizes are tax-free; savings interest is taxable above the personal savings allowance: £1,000 for basic-rate taxpayers, £500 for higher-rate, nothing at the additional rate. That single fact decides most cases. A higher-rate saver who has already used the allowance keeps 60p of every pound of interest, so a 4.35% prize rate is worth about 7.25% gross to them; a basic-rate saver whose interest sits inside the allowance keeps every pound and should compare rate with rate. Enter your own income and the interest you already earn, and the calculator finds your breakeven.
Mean, median and luck
The prize fund rate is an average, and the prize distribution is skewed by the large prizes: a typical holding earns a little less than the rate over a year, and a small holding may earn nothing. Capital is secure. For the rest of a savings decision (growth, the ISA allowance, and the 2027 savings rates) the savings growth calculator does the arithmetic.
Sources
- NS&I, Premium Bonds (prize fund rate and odds).
- HMRC, Tax on savings interest (personal savings allowance).