Premium Bonds vs Cash ISA — 2026 Expected Return Comparison
Premium Bonds are uniquely British — instead of paying interest, NS&I runs a monthly prize draw. Cash ISA pays predictable interest. Which actually returns more in 2026? Here’s the maths.
How Premium Bonds Work
You buy bonds from NS&I (£25 minimum, max £50,000 holding). Each £1 bond has a chance of winning a tax-free prize in the monthly draw. Prizes range from £25 to £1 million.
The prize fund rate is the headline number — it’s the equivalent average return if you held the average holding. In 2026 it’s about 4.15% (down from 4.65% in early 2025).
What “Average Return” Hides
The prize fund rate is calculated by assuming an average holding wins prizes at the average rate. In reality:
- Most holders win less than the prize fund rate
- A few win much more (including the £1M jackpots)
- Many small holders win nothing in a given year
The distribution is highly skewed. NS&I’s own calculator says that someone holding £10,000 in Premium Bonds has roughly:
- ~30% chance of winning more than the prize fund rate equivalent (£415+ in a year)
- ~50% chance of winning between half and the full rate
- ~20% chance of winning less than half
Holders of larger sums (£30k–£50k) tend to track closer to the average. Small holders (£1k–£5k) have more variance — they’re more likely to win nothing.
Cash ISA in 2026
- Easy-access: ~4.0% guaranteed (varies)
- 1-year fix: ~4.4%–4.6% guaranteed
The return is predictable. No skew.
The Tax Wrinkle
Premium Bonds prizes are tax-free for everyone — they always have been.
Cash ISA interest is tax-free — but for basic-rate taxpayers, the £1,000 Personal Savings Allowance covers most savings income anyway. So the “tax-free” advantage of Cash ISA is moot for many basic-rate savers.
For higher-rate taxpayers, the Cash ISA’s tax-free status matters more: £20,000 at 4.4% = £880 of interest. Outside an ISA, that £880 is taxed at 40% = £352 tax. Inside ISA: £0 tax.
Side-by-Side: £20,000 Holding in 2026
| Scenario | Premium Bonds | 1-yr fixed Cash ISA |
|---|---|---|
| Expected return | 4.15% (£830) | 4.5% (£900) |
| Range | £0 to £1M | £900 fixed |
| Tax | None | None |
| Liquidity | Withdraw anytime | Locked for 1 year |
| Compounding | None (winnings paid out) | Optional (rolls up at maturity) |
On a pure expected-value basis, the Cash ISA at 4.5% beats Premium Bonds at 4.15%. But Premium Bonds offer:
- Excitement of monthly draws
- Tax-free guaranteed (no PSA issue)
- Same-day withdrawal (Cash ISA easy-access matches this)
When Premium Bonds Make Sense
- You already have £20k in ISA wrapper used for the year
- You want a “fun” diversification within emergency fund
- You’re a basic-rate taxpayer with savings under £15k where PSA already shelters interest
- You have NS&I sentimental preference or want government-backed savings (Premium Bonds are 100% NS&I-backed, like all NS&I products)
When Cash ISA Beats
- You’re a higher or additional-rate taxpayer
- You’re disciplined about compounding (rolling over each year)
- You want predictable income or returns for budgeting
- You’re using the tax-free wrapper for long-term Cash ISA building
Bottom Line
For 2026 UK savers, the Cash ISA at top current rates marginally beats Premium Bonds on expected return — and the comparison gets more decisive for higher-rate taxpayers. Premium Bonds remain attractive as a diversifier or for the entertainment factor, but they shouldn’t be your sole savings vehicle. Use the ISA allowance first; bonds as supplementary.