Cash ISA vs Premium Bonds Calculator UK 2026 – Compare Returns

Updated 5 October 2026: Compare a Cash ISA interest rate with the current NS&I Premium Bonds prize-fund rate. This tool deliberately does not pretend it can predict your Premium Bonds winnings: prizes are random and the prize-fund rate is not an interest rate paid to each saver.

🎲 Cash ISA vs Premium Bonds Calculator

Compare known Cash ISA interest with the current Premium Bonds prize-fund-rate benchmark — without pretending random prizes are guaranteed.

Premium Bonds can be held from £25 up to £50,000 per person.
Enter the actual AER offered by the Cash ISA you are considering. Easy-access ISA rates can be variable.

12-month illustration

Cash ISA interest at entered AER£460.00
Premium Bonds 4.35% rate-equivalent£435.00
Rate-equivalent difference£25.00

Premium Bonds warning: The 4.35% annual prize-fund rate is used by NS&I to determine the overall prize fund. It does not mean your holding earns 4.35%. You might win nothing, less than this illustration, more than it, or a very large prize. The current odds are 21,000 to 1 for each £1 Bond in each monthly draw.
ISA allowance: The overall ISA subscription limit is £20,000 in 2026/27. So if this calculator shows a £30,000 or £50,000 savings pot, that does not mean you can necessarily put that whole amount into a Cash ISA as new subscriptions this tax year. Existing ISA money transferred correctly between providers is different.
Already announced for 6 April 2027: the Cash ISA subscription limit is due to become £12,000 for people under 65, within the £20,000 overall ISA limit. For people aged 65 or over, the Cash ISA limit remains £20,000.
Official sourcesNS&I Premium Bonds rates, odds and limits →GOV.UK ISA rules and 2026/27 allowance →Cash ISA limit change from April 2027 →
Important: This is an educational savings comparison, not financial or investment advice. It does not forecast Premium Bonds prizes or recommend one product. Check access terms, rate guarantees/variability, ISA eligibility and the latest NS&I information before moving savings.

Figures checked: 5 October 2026 • Premium Bonds: 4.35% prize-fund rate / 21,000-to-1 monthly odds per £1 Bond

Cash ISA vs Premium Bonds: what is the key difference?

A Cash ISA pays interest according to the account’s stated terms. Premium Bonds do not pay interest. Instead, every eligible £1 Bond is entered into NS&I’s monthly prize draw, where prizes are tax-free. That makes the two products fundamentally different even when their headline percentages look similar.

What is the Premium Bonds prize-fund rate in October 2026?

NS&I’s current Premium Bonds annual prize-fund rate is 4.35%, variable, with odds of 21,000 to 1 for every eligible £1 Bond in each monthly draw. The prize-fund rate is used to determine the overall amount available for prizes; it is not an interest rate credited to each account.

Why we removed the “median Premium Bonds return” prediction

It is tempting to turn the prize-fund rate into a predicted personal return, but that can be misleading. Premium Bonds prizes are distributed through a draw and include a small number of very large prizes. A saver can therefore experience a result very different from the overall prize-fund rate. This calculator shows the 4.35% rate only as a benchmark and does not label it as your expected, typical or median return.

How much can I hold in Premium Bonds?

NS&I allows an individual to hold up to £50,000 in Premium Bonds. The minimum purchase is £25. Newly purchased Bonds must normally be held for a full month before they become eligible for the monthly prize draw, so a brand-new holding does not necessarily receive 12 draw opportunities during its first 12 calendar months.

How much can I put into a Cash ISA in 2026/27?

The overall ISA subscription allowance is £20,000 for the 2026/27 tax year. That allowance is shared across the ISA types you subscribe to. Money already inside the ISA system can be transferred between providers using the ISA transfer process without being treated in the same way as withdrawing it and making a fresh subscription.

What changes to Cash ISAs in April 2027?

From 6 April 2027, the Cash ISA subscription limit is scheduled to be £12,000 for people under age 65, while the overall ISA limit remains £20,000. People aged 65 or over retain a £20,000 Cash ISA limit. This page is dated because that change matters when comparing how much new money can be sheltered in cash.

Are Cash ISA interest and Premium Bonds prizes tax-free?

Interest earned inside a Cash ISA is tax-free. NS&I states that Premium Bonds prizes are also free from UK Income Tax and Capital Gains Tax. This means tax is not the main distinction between these two products; certainty of return, access terms, rates and the chance-based nature of Premium Bonds are more relevant differences.

Is a Cash ISA return guaranteed?

Do not assume every Cash ISA rate is fixed. Fixed-rate Cash ISAs normally lock a rate for a stated period but can restrict access, while easy-access Cash ISA rates are commonly variable and can change. The calculator therefore asks you to enter the actual AER of the account you are comparing rather than claiming there is one universal “best Cash ISA rate”.

Important information

This calculator is designed to explain the arithmetic and product differences, not tell you where to save. Rates can change, Premium Bonds winnings are random, and account terms differ. Always check the current provider terms and official NS&I/HMRC information before acting.