Premium Bonds can beat low bank rates for spare cash.
They work best when the NS&I prize‑fund is higher than your Cash ISA rate.
Premium Bonds also suit savers who pay tax on interest and want tax‑free upside.
Savers facing low bank rates: when to choose premium bonds
A short checklist helps decide: time horizon, ISA allowance, tax band and need for reliable income.
Each item changes which product is better for the saver.
Time horizon and purpose
The purpose of the funds defines the choice.
Emergency money needs predictability and ready access.
Money for a discretionary play pot can accept variable returns.
ISA allowance and tax band
The annual ISA allowance is £20,000 for 2024/25.
This allowance protects interest inside the ISA wrapper.
The Personal Savings Allowance for 2024 leaves basic‑rate savers £1,000 tax‑free interest and higher‑rate savers £500.
Check processing times online before you move funds.
Liquidity and access
NS&I lets you submit a redemption online quickly.
NS&I processes redemptions promptly, but bank transfers can take a few working days.
Large redemptions may need ID checks that add delay.
Treat a redemption as quick to start but expect settlement in a few working days.
Cash ISAs can be instant, on notice, or fixed term.
Small balances and short horizons
For small balances follow a simple rule.
Treat Premium Bonds as a tax‑free chance play for spare cash.
Use a Cash ISA for an emergency pot.
Expected value for £1k and £10k
Use two prize‑fund scenarios to compare outcomes: 1.0% and 3.0%.
At 1.0% the expected annual return is £10 on £1,000 and £100 on £10,000.
At 3.0% expected return is £30 on £1,000 and £300 on £10,000.
Compare to typical cash ISA rates
If a Cash ISA pays 1.5% the saver gets £15 per year on £1,000 and £150 per year on £10,000.
The ISA gives steady, guaranteed interest and compounds.
Premium Bonds give variable payouts that may be zero in a year.
Practical rule for small savers
If money is needed within 1–3 years and certainty matters, favour a Cash ISA or notice account.
If the saver treats some cash as optional and values tax‑free upside, hold a small amount in Premium Bonds.
Keep the emergency pot separate from chance bets.
For a £1,000 holding the expected annual Premium Bonds return at a 1% prize fund is about £10. That average hides the fact many individual savers win nothing in a year.
Larger balances and longer horizons
Large holdings change the maths.
The probability of at least one prize rises with more bonds.
Expected value still equals the prize‑fund rate times the holding.
Concentration risk and lost compounding can also matter.
Expected value for £50k
With a 1.0% prize fund the expected return on £50,000 is about £500 per year.
With a 3.0% prize fund the expected return is about £1,500 per year.
These are averages across all bondholders and not guarantees for any saver.
Probability and distribution
The chance of at least one prize increases with more bonds but wins remain random.
Use formula 1−(1−p)^N where p is per‑bond monthly win chance and N is number of bonds.
Opinion with nuance
The error most guides make is treating the prize‑fund rate as guaranteed interest.
Premium Bonds suit an overspill of cash if the saver treats the holding as a low‑risk lottery.
Capital is safe, prizes are tax‑free and liquidity is good, but returns are unpredictable.
This works well when a core emergency pot sits in a Cash ISA or FSCS‑protected accounts.
Use ISA allowance for funds that need compound growth.
Bigger holdings reduce variance but do not ensure big wins.
A common error is treating the prize‑fund rate as if it were guaranteed interest.
Many guides compare headline prize‑fund rates with bank rates without using expected‑value math.
This misleads savers because most bondholders win nothing in a year.
What to avoid
Do not use Premium Bonds for predictable regular income to cover expenses.
Do not use them for long‑term growth; use a Stocks & Shares ISA instead.
Avoid Premium Bonds when inflation is high and erodes real returns.
If ISA allowance is unused, moving money into a Cash ISA often beats Premium Bonds for steady returns.
Premium Bonds are liquid but redemptions can take a few working days and may need ID checks.
What to do now
Preserve an emergency pot in a Cash ISA or FSCS‑covered accounts equal to three months of essential expenses.
Use any unused ISA allowance for sums that should earn predictable compound interest.
Put some spare cash into Premium Bonds only if tax‑free upside matters and variable returns are acceptable.
Consider 10–30% of non‑core savings as a starting allocation.
Run the calculator in the Tools section with current prize‑fund and ISA rates and your inflation estimate.
Then choose a split that keeps the core emergency fund intact.
Account for inflation and tax
Inflation materially alters the comparison because real return depends on nominal yield and the price level.
Use the real‑rate formula (1 + nominal)/(1 + inflation) − 1 to convert nominal rates to real terms.
For example, on £10,000 a 1.5% Cash ISA with 3.0% inflation gives a real return of roughly −1.46% (about −£146).
A 1.0% expected Premium Bonds return in the same environment is about −1.94% (about −£194).
For a £1,000 emergency pot these rates imply real losses near −£15 and −£19 respectively.
For £50,000 the same rates imply roughly −£730 and −£970.
Presenting these pound‑value real returns helps savers see that both options can lose purchasing power in high inflation.
Tax status changes the arithmetic in ways many guides underplay.
A basic‑rate taxpayer benefits from a £1,000 Personal Savings Allowance.
So modest bank interest may already be tax‑free for that saver.
Include tax in your calculations before deciding.
A simple calculator helps compare ISA interest and Premium Bonds expected value.
Paste the small script below into the browser console to test numbers quickly.
Javascript
// Simple ISA vs Premium Bonds calculator
var holding = 10000; // amount in pounds
var prizeFund = 0.01; // example 1.0% as decimal
var cashIsaRate = 0.015; // example 1.5% as decimal
var inflation = 0.03; // example 3.0% as decimal
var expectedPremium = holding * prizeFund;
var cashIsaNominal = holding * cashIsaRate;
var premiumReal = holding * ( (1 + prizeFund) / (1 + inflation) - 1 );
var isaReal = holding * ( (1 + cashIsaRate) / (1 + inflation) - 1 );
console.log('Holding: £' + holding);
console.log('Expected Premium (nominal): £' + expectedPremium.toFixed(2));
console.log('Cash ISA (nominal): £' + cashIsaNominal.toFixed(2));
console.log('Premium (real): £' + premiumReal.toFixed(2));
console.log('Cash ISA (real): £' + isaReal.toFixed(2));
Quick visual: prize probability by balance
Below is a compact infographic showing how the chance of wins rises with balance.
Replace numbers with current per‑bond odds for precise planning.
Probability of at least one monthly win (illustrative)
£1,000 (approx)
£10,000 (approx)
£50,000 (approx)
Bars are illustrative. Use the calculator with current per‑bond odds from NS&I for exact probabilities.
An interactive comparator lets a saver enter Cash ISA rates, the NS&I prize‑fund rate and holding.
This shows how sensitive the choice is to small rate changes.
For a £10,000 holding, a 1.5% Cash ISA produces £150 nominal per year.
If the prize fund rises to 2.0% the expected Premium payout becomes £200 and overtakes the ISA.
Showing side‑by‑side nominal and expected outcomes with toggles for tax and inflation makes the choice numeric.
Comparative table: premium bonds vs cash ISA
| Feature |
Premium |
Cash ISA |
| Return type |
Variable prizes; expected value ≈ prize‑fund rate |
Guaranteed interest rate set by provider |
| Tax treatment |
Prizes tax‑free; outside ISA allowance |
Interest tax‑free within ISA allowance |
| Capital protection |
Backed by HM Treasury (NS&I) |
Usually FSCS protected up to £85,000 per institution |
| Liquidity |
High; online redemptions may take a few days |
Varies: instant, notice or fixed term |
The annual ISA allowance is £20,000 (2024/25). Banks and building societies are FSCS covered up to £85,000 per institution (2024). The Personal Savings Allowance lets basic‑rate savers have £1,000 tax‑free interest and higher‑rate savers £500.
Practical cases and a common scenario
A common case: a saver moved £10,000 into Premium Bonds expecting about £300 the first year and received £0.
This outcome happens often because expected value spreads across all holders and many get nothing annually.
This data point shows the mistake most guides overlook.
They compare prize‑fund rates as if those rates were fixed interest.
A saver who needs steady cash flow should not choose Premium Bonds for that purpose.
To test exact scenarios run the calculator in the Tools section with actual prize‑fund and ISA rates and your inflation estimate.
Then compare nominal and real results.
For official prize‑fund odds and current NS&I terms consult NS&I and for inflation figures see ONS.
If unsure, run the numbers or seek independent financial advice for your situation.
Frequently asked questions
Is it better to buy premium bonds or an ISA?
If the saver has unused ISA allowance and wants reliable compound interest, the Cash ISA usually wins.
Premium Bonds can be attractive for spare cash when the saver values tax‑free upside and liquidity or has no ISA room.
What are the odds of winning with £50,000?
The expected annual payout equals the prize‑fund rate times £50,000 as an average across holders.
Probability of at least one win grows with more bonds but does not guarantee large prizes.
Do premium bonds use ISA allowance?
No. Premium Bonds sit outside the ISA allowance and prizes remain tax‑free irrespective of ISA status.
This lets a saver hold both a Cash ISA and Premium Bonds at the same time.
Are premium bonds safe compared to bank accounts?
Both are low risk.
Bank and building society deposits are generally FSCS protected up to £85,000 per institution.
NS&I is backed by HM Treasury and is considered secure.
The key difference lies in return predictability, not capital safety.
How does inflation affect the decision?
Higher inflation reduces the real return of both Cash ISAs and Premium Bonds.
If inflation exceeds nominal gains the saver faces a negative real return.
Such savers should consider longer‑term investments for growth.
What about junior accounts: junior ISA vs premium?
A Junior ISA compounds tax‑free for the child and uses the child’s allowance, making it better for long‑term savings.
Junior Premium Bonds keep funds liquid and tax‑free but give variable returns.
Split small gifts between the two depending on horizon.
