Premium Bonds Explained: How They Work and What Your Odds Really Are
Premium Bonds swap savings interest for a monthly shot at tax-free prizes, but understanding the odds helps you judge whether that trade-off suits you.
What Premium Bonds actually are
Premium Bonds are a savings product run by NS&I (National Savings and Investments), which is backed by the UK government. Instead of paying interest in the normal way, NS&I pools the interest that would have been earned on all bonds and uses it to fund a monthly prize draw. Every £1 you put in buys one bond, each with its own unique number, and each bond is entered into the draw once it has been held for a full calendar month.
There is a minimum purchase amount and a maximum total holding per person, both set by NS&I and reviewed from time to time, so check the current limits on the NS&I website before you buy. Because Premium Bonds are not a normal savings account, they do not pay a fixed rate of interest. Instead, NS&I sets an annual ‘prize fund rate’, which is used to estimate the average return across all bondholders, but any individual saver could win nothing at all, or could win considerably more than that average implies.
How the prize draw works
Each month, a computer system commonly referred to as ERNIE (Electronic Random Number Indicator Equipment) generates random numbers that are matched against eligible bond numbers to select winners. The draw is independently checked, and prizes range from small amounts up to two jackpot-sized prizes each month. All prizes are tax-free, which is one of the main attractions for higher and additional rate taxpayers who have used up their Personal Savings Allowance.
Winnings can typically be paid directly into your bank account, reinvested into more bonds, or held in your NS&I account, depending on the option you choose when you apply. You can check whether you have won through the NS&I website or app, and unclaimed prizes remain payable indefinitely, so it is worth checking old holdings if you or a family member has bonds that have been forgotten about.
The odds, and why they are the same for everyone
NS&I publishes odds of winning per £1 bond for each monthly draw, and this figure changes over time as the prize fund rate and total number of bonds in the draw change. Crucially, the odds are per bond, not per person. If you hold more bonds, you get more entries into the draw, so your overall chance of winning something in a given month rises roughly in line with how much you hold, up to the maximum permitted holding.
This means a saver near the maximum holding is statistically far more likely to win one or more prizes most months than someone holding a small amount. Someone with a modest holding might go many months, or even years, without winning anything, even though the published odds sound reasonably favourable. This is simply how probability works when a huge prize fund is spread across billions of individual bond numbers; small holdings can easily sit outside the statistical average for long stretches.
Why the ‘average return’ can be misleading
NS&I’s headline prize fund rate is often compared to easy-access savings rates, but this comparison only really holds true over a very large number of bonds and a long period of time, similar to how a casino’s average payout rate does not tell you what any one player will experience on a given night. In practice, individual results vary widely. Some savers with average-sized holdings beat the headline rate in a good year, while others fall well short, sometimes winning nothing at all.
This variability is the core trade-off of Premium Bonds: you give up the certainty of a fixed interest rate in exchange for the tax-free chance of a larger prize, with your original capital remaining safe because it is backed by the UK government through NS&I. For anyone who dislikes uncertainty, or who needs predictable income from their savings, a normal savings account or ISA may be more suitable. For those who are comfortable with the lottery-style element and want a low-risk home for money they do not need immediate interest from, Premium Bonds can be a reasonable complement to other savings.
What to check before you buy
Before investing, check the current minimum and maximum holding limits, the current prize fund rate, and the current odds of winning per £1 bond directly on the NS&I website, since all of these are reviewed periodically and the figures you may see elsewhere can quickly go out of date. It is also worth comparing the effective potential return against current best-buy savings rates listed by independent comparison services, and considering whether you have unused Personal Savings Allowance or ISA allowance that might make a conventional savings product more tax-efficient for your circumstances.
Finally, remember that Premium Bonds do not grow in value the way an investment might, since your capital is not going up in the market. Your original amount stays the same in cash terms, and your total return depends entirely on which, if any, prizes your bonds are randomly matched to during the months you hold them.