Your Cash ISA Pays 4.68% Guaranteed — Premium Bonds Can't Promise You a Single Penny

Premium Bonds don't pay interest. They enter your money into a monthly prize draw. NS&I quotes a 3.60% "prize fund rate" — but that's the total prize pool as a percentage of all bonds in issue. It's an average across every bondholder in the country, not a promise to any individual.

The median bondholder does worse than the headline rate. With odds of 22,000 to 1 per £1 bond, someone holding £1,000 has roughly a 55% chance of winning nothing at all in any given month. Over a full year, their expected return is about £36 — but the actual return could easily be £0, £25, or £75. There's no floor, no minimum, no guarantee.

A cash ISA paying 4.68% on £1,000 earns £46.80. Guaranteed. Credited to your account. No luck required. That's the fundamental difference: a cash ISA pays you what it says on the label. Premium Bonds pay you what the random number generator decides.

The variance problem gets worse at smaller holdings. Premium Bonds need at least £10,000-£20,000 before the law of large numbers starts working in your favour. Below that, you're essentially gambling your savings returns on a monthly lottery. With a cash ISA, whether you deposit £100 or £20,000, you earn the stated rate. Full stop. The gov.uk ISA page confirms the £20,000 annual allowance.

NS&I is cutting the Premium Bonds prize fund rate to 3.30% from April 2026, with odds lengthening to 23,000 to 1. Meanwhile, cash ISA rates remain competitive — easy-access ISAs pay up to 4.68%, and one-year fixed ISAs offer up to 4.32%.

That's a gap of 1.38 percentage points between the best easy-access cash ISA and Premium Bonds from April. On £20,000, the difference is £276 per year you're leaving on the table by choosing Premium Bonds.

The Bank of England base rate sits at 3.75% after six consecutive cuts from the 5.25% peak. Cash ISA providers have been slower to cut rates than NS&I — creating the widest gap between ISA rates and Premium Bonds that we've seen in years. NS&I must balance between offering competitive rates to savers and not drawing too much money away from commercial banks. That structural constraint means NS&I rates will almost always lag the best cash ISA deals.

Here's a data point that crystallises the problem: 75% of cash ISAs on the market currently offer above-inflation returns, according to Moneyfacts. Premium Bonds at 3.30% from April may not even clear CPI. You're accepting a below-inflation return for the privilege of a lottery ticket. NS&I publishes the latest prize fund rate and odds.

The ISA allowance doesn't roll over. If you don't use your £20,000 by 5 April 2026, it's gone permanently. Premium Bonds have no such deadline — you can buy them any day of the year.

But that flexibility is a trap. It encourages procrastination. "I'll buy Premium Bonds next month" costs you nothing in deadline terms but everything in compound returns. The ISA deadline forces action — and action is what builds wealth.

Here's the five-year calculation that should settle this debate for most people: £20,000 into a cash ISA at 4.68% today, with rates gradually declining to 3.5% over five years, generates roughly £4,200 in compound tax-free interest. The same £20,000 in Premium Bonds at the declining prize fund rate (3.60% dropping to 3.30% and likely lower) generates an expected £3,100 — assuming you're average. If you're unlucky, considerably less.

That's over £1,100 of additional tax-free income from choosing the ISA. Not over a lifetime — over just five years. Compound that across a decade of annual £20,000 contributions and the gap becomes tens of thousands of pounds.

For our full breakdown of ISA types and strategies, our ISA hub covers every wrapper. And for more on locking in today's rates, see our guide on fixed-rate cash ISAs. Compare options on our savings hub.

From April 2027, cash ISA contributions for under-65s drop to £12,000 per year. Some argue this makes Premium Bonds more attractive as an overflow. They're wrong about the sequencing.

The cap makes each year's cash ISA allowance more precious, not less. Once inside the ISA wrapper, your money earns tax-free interest forever — not just while you hold it. A £20,000 cash ISA opened this April continues earning tax-free returns for decades, regardless of what happens to future allowances. That compound tax-free growth is the ISA's superpower, and it's something Premium Bonds structurally cannot replicate.

Premium Bonds offer tax-free prizes, true. But there's no wrapper effect. No compounding of tax-free gains year after year. Each month's draw is independent — your prizes don't earn more prizes. In a cash ISA, your interest earns interest, all sheltered from HMRC indefinitely.

If you have £20,000 to shelter this tax year and only £12,000 from next year, the rational move is obvious: max out the cash ISA now while the full £20,000 is available. Premium Bonds are fine for whatever you can't fit in an ISA — but they're a second choice, not a first.

For those weighing other savings options, our hub compares every product available to UK savers.

Additional-rate taxpayers sitting on more than £50,000 in cash, who've already maxed their ISA, and who want government-backed security above the FSCS £85,000 limit. That's a real but narrow group.

For everyone else — basic-rate taxpayers with the full £1,000 personal savings allowance, people with unused ISA allowance, anyone with less than £20,000 to save — a cash ISA is the strictly better product. The returns are higher, the returns are predictable, and the tax wrapper compounds in your favour over time.

The emotional appeal of Premium Bonds is real. The monthly prize draw creates excitement that a savings statement never will. But excitement is not a financial strategy. At current rates, choosing Premium Bonds over a cash ISA is paying roughly 1.4 percentage points per year for the thrill of checking whether ERNIE picked your number.

There's also a sunk cost problem. Many people hold Premium Bonds because they've always held Premium Bonds — an inheritance from grandparents, a childhood gift. Nostalgia isn't an investment thesis. If those bonds are sitting there instead of an ISA, they're costing you real money every year.

Our recent ISA deadline article breaks down exactly how to use every pound of your allowance before April 5.

This article is for informational purposes only and does not constitute financial advice. You should seek independent financial advice before making any investment decisions.