Premium Bonds vs a Cash ISA: Which Gives You a Better Return?

Premium Bonds are the UK’s single most popular savings product, held by over 22 million people - but they don’t pay interest in the conventional sense, which makes comparing them to a Cash ISA trickier than it first appears. Here’s how the maths actually works.

How Premium Bonds actually work

Premium Bonds, from NS&I, don’t pay interest. Instead, every £1 Bond is entered into a monthly prize draw, with tax-free prizes ranging from £25 up to two £1 million jackpots each month. The prize fund rate - currently 3.8% from the July 2026 draw, up from 3.3% previously - represents the average return across all Bond holders, not a guaranteed personal return. In an average month, a typical holder with average luck may win nothing at all.

• Minimum holding: £25
• Maximum holding: £50,000 per person (including bonds held for children under 16)
• Odds per £1 Bond: 22,000 to 1 for each monthly draw, from the July 2026 draw
• All prizes are entirely tax-free, regardless of your tax band
• 100% backed by HM Treasury, with no upper limit on the security of your money - unlike standard bank deposits, which are protected only up to £120,000 under the Financial Services Compensation Scheme

The maths on a typical holding

At the new 3.8% prize fund rate, someone holding the maximum £50,000 might expect somewhere in the region of £1,900 a year in prizes on average - but actual results vary enormously due to the random nature of the draw, and a saver with smaller holdings faces meaningfully higher odds of winning nothing at all in a given year. An AJ Bell Freedom of Information analysis found fewer than 1% of Premium Bond prizes go to holders with less than £1,000 saved, reflecting how the maths favours larger holdings even before luck is considered.

How this compares to a Cash ISA

A Cash ISA pays a guaranteed interest rate, known in advance, with no randomness involved. As of mid-2026, average 1-year fixed-rate Cash ISAs have been running well above the 3.8% Premium Bonds prize fund rate, and even average variable Cash ISA rates have sometimes come close, depending on the provider - meaning a saver purely optimising for guaranteed return often does better with a competitive Cash ISA than with Premium Bonds. For an even higher guaranteed rate on money you can pay in gradually rather than as a lump sum, regular saver accounts have quietly offered some of the best rates in the entire savings market through 2026, albeit with much lower monthly deposit caps than a full Cash ISA allowance.

Where Premium Bonds still make sense

• Additional-rate taxpayers with no Personal Savings Allowance at all, for whom Premium Bonds’ fully tax-free prizes can be more attractive than fully taxable savings interest - though a Cash ISA achieves the same tax-free outcome with a guaranteed rather than random return.
• Savers who enjoy the lottery-style appeal and are comfortable trading a small amount of expected return for the (small) chance of a life-changing prize.
• Very large holdings, where the statistical spread of outcomes narrows and the realised return gets closer to the headline prize fund rate.
• Anyone who has maxed out their Cash ISA allowance for the year and wants another fully tax-free option for additional savings.

A key risk often overlooked

Because Premium Bonds pay no guaranteed return, there’s a genuine risk that your money loses purchasing power to inflation if you’re unlucky over an extended period - CPI inflation stood at 2.8% in the 12 months to May 2026, meaning a saver winning nothing, or winning less than that rate, is effectively losing real value each year, a risk a guaranteed-rate Cash ISA doesn’t carry in the same way.

The bottom line

For most savers purely optimising for the best expected return, a competitive Cash ISA currently beats Premium Bonds on the numbers alone. Premium Bonds remain a reasonable choice for additional-rate taxpayers, very large holdings, or savers who value the tax-free prize element and are comfortable with the randomness involved - but they shouldn’t be assumed to be automatically better simply because they’re popular.