Premium Bonds — what they actually are
Tax-free, government-backed, can win up to £1m, can also win nothing for years. Here's the actual mechanic and when they make sense versus when a Cash ISA quietly does better.
Premium Bonds are an NS&I product. You buy bonds in £1 units — minimum £25, maximum £50,000 — and each bond is entered into a monthly prize draw. Prizes range from £25 to £1 million and are tax-free. Your bonds keep their face value (so you can't lose the original capital), and you can cash them out within a few days.
The advertised "prize fund rate" (currently around 4%) is the average return across all bondholders combined. It's the long-run average, not a yield on your specific holding. Smaller holdings can win much more or much less, depending on luck.
How they typically compare to a Cash ISA
Illustrative — £{exampleHolding.toLocaleString()} held for 1 year
Cash ISA at 4.5%: ~£450 interest, tax-free, predictable
Premium Bonds at 4% prize fund rate: ~£400 expected over time, but for most months you'll win nothing
On expected return, a good Cash ISA usually wins. The Premium Bonds case isn't about expected return — it's about lottery upside, tax-free status for bigger holdings, and the fun.
When Premium Bonds make sense
Three situations. First, you're a higher-rate taxpayer who has already used your £500 Personal Savings Allowance and any further interest in regular savings would be taxed at 40%. PB winnings are tax-free, so the comparison shifts in their favour.
Second, you've already maxed your ISA allowance for the year and want a tax-free home for additional cash. PBs sit alongside ISAs — they don't use up the £20k allowance.
Third, you genuinely enjoy the lottery upside. There's no financial argument for this, but it's real and it's why some people prefer them to a Cash ISA paying a higher headline rate.
When they don't
Holdings under about £10,000 statistically underperform the prize fund rate — you might go many months without winning anything, while a Cash ISA pays you predictable interest every month. If your ISA allowance isn't used and you're a basic-rate taxpayer with the Personal Savings Allowance still intact, the maths almost always points to a Cash ISA or a regular savings account first.
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