Key takeaways
Both premium bonds and ISAs are tax-efficient savings options for UK residents -- premium bonds prizes are tax-free, and ISA returns (interest or investment gains) are sheltered from income and capital gains tax.
The key difference is certainty: a cash ISA offers a guaranteed interest rate; premium bonds offer a chance of winning prizes with no guaranteed return.
Premium bonds are backed 100% by HM Treasury with no limit. Cash ISA deposits are protected up to 85,000 pounds per institution under the FSCS.
The annual ISA allowance for 2026/27 is 20,000 pounds. Premium bonds have a maximum holding of 50,000 pounds per person with no annual contribution limit.
For large savings pots where tax on interest is a concern, the comparison depends on the premium bonds prize fund rate versus available ISA rates at the time of decision.
Reviewed: June 2026Key facts
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The fundamental difference: certainty vs chance
A cash ISA pays a stated interest rate that is either fixed for a term or variable but predictable. If you deposit 10,000 pounds into a cash ISA at 4% AER, you will receive approximately 400 pounds in interest after one year. The return is known in advance.
Premium bonds pay no guaranteed return. The prize fund rate -- set by NS&I -- determines the total prizes available across all bonds, but an individual holder may win significantly more than that rate implies, significantly less, or nothing at all in a given year. The outcome is determined entirely by random selection.
Tax treatment
Both options are tax-efficient. Premium bonds prizes are entirely tax-free -- there is no income tax or capital gains tax on any prize amount. ISA returns (interest on cash ISAs, or investment returns on stocks and shares ISAs) are sheltered from income tax and capital gains tax within the ISA wrapper.
Outside a tax wrapper, savings interest above the Personal Savings Allowance (1,000 pounds for basic rate taxpayers, 500 pounds for higher rate taxpayers in 2025/26) is subject to income tax. For savers with large deposits who might exceed the PSA, both options offer a route to tax-free returns.
Which is better for large savings pots
For savers holding amounts above the Personal Savings Allowance threshold -- where interest on a standard savings account would attract income tax -- both premium bonds and ISAs provide tax shelter. The decision between them depends on the prize fund rate versus available ISA rates, and how much variance in return the saver is comfortable with.
If the premium bonds prize fund rate is broadly equal to available cash ISA rates, a saver with a large holding might prefer premium bonds for the upside potential (a 1 million pound jackpot, however statistically unlikely) combined with 100% government backing. A saver who needs certainty -- for example to plan income in retirement -- would typically prefer a fixed-rate cash ISA.
Access and flexibility
Cash ISAs vary in access terms. Easy-access cash ISAs allow withdrawals at any time without penalty. Fixed-rate cash ISAs lock the money in for a term (typically 1, 2 or 5 years) in exchange for a higher guaranteed rate. Early withdrawal from a fixed-rate ISA typically incurs a penalty equivalent to a number of days interest.
Premium bonds can be cashed in at any time. There is no fixed term, no notice period required and no penalty for encashment. NS&I typically processes encashment requests within 3 to 5 working days and transfers the funds to a registered bank account.
Stocks and shares ISA: a different comparison
A stocks and shares ISA invests in equities, bonds or funds rather than holding cash. Over long periods stocks and shares ISAs have historically produced higher returns than cash savings, but they carry investment risk -- the value can fall as well as rise. Premium bonds carry no investment risk: the original amount is always returned in full.
For savers with a long time horizon (10 years or more) and tolerance for short-term volatility, a stocks and shares ISA has historically outperformed cash savings and premium bonds. For savers who need capital certainty -- no possibility of losing the original investment -- premium bonds and cash ISAs are the relevant comparison.
Suitability: which to choose
Premium bonds suit savers who want government-backed security beyond the 85,000 pound FSCS limit, are comfortable with variable and uncertain returns, and value the possibility of a large prize win. They work well as part of a broader savings strategy rather than as the sole savings vehicle.
Cash ISAs suit savers who need a predictable return, are planning for a specific goal with a known time horizon, or want to lock in a rate before expected interest rate falls. Fixed-rate ISAs are particularly appropriate when rates are high and expected to fall.
Many financial planners suggest holding both -- using the ISA allowance for reliable tax-free returns and premium bonds for the 50,000 pound maximum as a tax-efficient, government-backed emergency fund or additional savings pot with prize upside.
Related guides
Disclaimer: This guide is for informational purposes only. Kael Tripton Ltd is not regulated by the FCA and does not provide regulated financial advice. Premium bonds are provided by NS&I, a government-backed savings institution. Always verify current prize rates and terms directly at nsandi.com before making savings decisions.
Frequently asked questions
Are premium bonds better than an ISA?
Neither is universally better -- it depends on the saver's circumstances. Premium bonds offer 100% government-backed security with no guaranteed return. Cash ISAs offer guaranteed interest rates with FSCS protection up to 85,000 pounds. For large savings pots above the Personal Savings Allowance threshold, both shelter returns from tax. The choice depends on whether the saver prioritises certainty of return (ISA) or government backing beyond the FSCS limit combined with prize upside (premium bonds).
Can I have both premium bonds and an ISA?
Yes. Having premium bonds does not affect your ISA allowance and vice versa. Many UK savers hold both simultaneously. The annual ISA allowance is 20,000 pounds in 2026/27. The premium bonds maximum holding is 50,000 pounds per person.
Do premium bonds count as ISA allowance?
No. Premium bonds are not an ISA and do not use or reduce your annual ISA allowance. They are separate savings products. You can hold the maximum 50,000 pounds in premium bonds and still use your full 20,000 pound ISA allowance in the same tax year.
What is the effective interest rate on premium bonds?
Premium bonds do not pay interest -- they pay prizes. The prize fund rate set by NS&I represents the equivalent annual return if the prizes were distributed evenly, but individual returns vary widely due to random selection. NS&I publishes the current prize fund rate at nsandi.com.
Are premium bonds safe?
Yes. Premium bonds are backed 100% by HM Treasury with no upper limit on the amount protected. Unlike bank deposits which are covered by the FSCS up to 85,000 pounds per institution, NS&I products including premium bonds carry an unlimited government guarantee. The original investment is always returned in full on encashment.
