£20,000 can sit in Bonds for a year and still win nothing. That is the uncomfortable trade-off many savers miss: the money feels safe, but the return is uncertain. For anyone comparing a cash ISA, a market ISA, or NS&I products, the real question is not whether the capital is protected, but whether the payout is predictable enough to justify the gamble.
Bonds do not offer a guaranteed return, so they can lag a cash ISA when the aim is steady growth, easy access and a realistic idea of what £5,000, £20,000 or £50,000 might earn. A market ISA may still come out ahead in practice if the holding period is long enough and the expected return beats the prize odds.
Premium bonds do not guarantee a return
People often feel safe because the money is not at risk in the way shares are. That is only half the story. The other half is that you may earn nothing in a month, or win a prize that looks generous on paper but still leaves you behind a plain savings rate over the year.
The current NS&I Bonds prize fund rate is 4.00% currently, but that is not the same as a 4.00% interest rate on your balance. It is an average across all holders, shaped by monthly prize draws and the odds of each £1 Bond winning.
NS&I says the odds are 22,000 to 1 for each £1 Bond in each monthly draw, which is why the return can feel lumpy rather than smooth. NS&I Bonds
Prize draws replace interest
The mistake most often made here is simple. People read the prize fund rate and treat it like interest. It is not interest. It is more like buying raffle tickets where the prizes come from the same pot, only the prize pot is split across many holders.
A saver with £5,000 in Bonds holds 5,000 £1 entries. That sounds like a lot, but the monthly result still depends on luck. One person may win £50 twice in a year. Another may win nothing at all.
The prize fund rate is an average, not a promise. That line matters because averages do not pay bills. Cash in hand does.
Expected return is not the same as personal outcome
Expected return means the average outcome over a very large number of savers and draws. It does not mean your own account will hit that number. A Cash ISA works the other way around. If it pays 4.25%, the saver knows what £5,000 should earn over a year, aside from rate changes on variable accounts.
This works well in theory, but in practice many people want two things at once: safety and a known result. Bonds give the first and not the second. A Cash ISA gives both, if the rate is fixed or clearly published and the account terms stay stable.
Bonds protect the amount you put in, but they do not protect the return you get back.
Probabilities matter because Bonds do not pay the same way every month. NS&I’s odds of 22,000 to 1 per £1 Bond in each monthly prize draw mean many holders will see long stretches with no meaningful payout, even if the annual prize fund rate looks competitive on paper. A saver with £20,000 has 20,000 entries, but that still does not guarantee a return close to the average in a single year. Expected return is a statistical concept, while the cash outcome is personal and uneven.
That is why a cash ISA with a fixed or clearly published interest rate can be better for planning: the saver knows the savings rate in advance, whereas Bonds only offer the possibility of tax-free prizes.
Key takeaways: when each option wins
The best choice depends on what the money has to do. If the money must grow in a predictable way, a guaranteed-return account usually wins. If the saver likes the chance of a tax-free prize and accepts uneven results, Bonds can still make sense. If the goal is long-term growth, a market ISA may be the better tool.
For £5,000, £20,000 and £50,000, the picture changes a lot. The numbers are not glamorous, but they are the ones that matter. A small balance often favours a decent Cash ISA. A larger balance can improve the chance of winning with Bonds, yet it still does not remove randomness.
£5,000 favours certainty
With £5,000, a Cash ISA paying 4.25% would produce about £212.50 a year before any rate change. Bonds may pay more, less, or nothing in cash terms from month to month. The saver gets a chance at prizes, but the average outcome is still not as neat as a savings rate.
A basic-rate taxpayer with room inside the personal savings allowance may not need the ISA wrapper at all for a small balance. HM Revenue and Customs sets a personal savings allowance of £1,000 for basic-rate taxpayers and £500 for higher-rate taxpayers. That means a simple taxable account can still be fine for some savers, depending on the rate and their wider income. HMRC savings interest rules
£50,000 changes the odds
At £50,000, Bonds give 50,000 monthly entries. That improves the chance of winning something, but it does not create a guaranteed yearly return. The saver may win several prizes and do well. Another saver with the same balance may do less well for a long stretch.
A Cash ISA on £50,000 at 4.25% would pay about £2,125 a year if the rate stayed still. That is the clean comparison. Bonds need a strong run of prize luck to beat that kind of predictable outcome.
£50,000 in Bonds gives more chances, not a better promise.
When a market ISA wins in practice
A Stocks and Shares ISA can beat Bonds when the money stays invested long enough for growth to outweigh charges and volatility. That usually means years, not months. If the portfolio returns 5% a year after costs and inflation runs lower, the gap can be meaningful.
The catch is obvious. Shares can fall. A market ISA suits a saver who can tolerate short-term drops and does not need the cash on a fixed date. If the money must be there in 12 months, the numbers can turn ugly fast.
A useful way to judge Bonds against a market ISA is to run the same money through both paths over the same period. For example, £50,000 in Bonds gives 50,000 £1 entries each month, but the prize fund rate is still only an average, not a promise. By contrast, a market ISA invested in a diversified portfolio might aim for 5% a year before fees, or around 4% after charges in a moderate-cost setup. Over five years, that can make a real difference: £50,000 growing at 4% a year compounds to about £60,833, while Bonds could end up above or below that depending on prize luck.
The larger the balance and the longer the horizon, the more the expected return of the market ISA can outweigh the randomness of the monthly prize draw.
Use this comparison to choose faster
The fastest way to choose is to compare three things side by side: certainty, access and expected return. Bonds score well on capital safety and tax treatment, but poorly on predictability. Cash ISAs score well on predictability and access. Stocks and Shares ISAs score well on long-term growth and poorly on short-term certainty.
The Financial Conduct Authority reminds consumers that cash savings and investments are different products with different risks. The Financial Services Compensation Scheme also protects eligible cash deposits up to £85,000 per person, per authorised firm, which matters when comparing a bank account with NS&I's state-backed structure. FCA savings and investments guidance
Decision matrix for savers
| Product |
Return type |
Capital safety |
Tax treatment |
Access |
Best fit |
| Premium |
Prize-based, not guaranteed |
Capital protected by NS&I |
Tax-free prizes |
Usually flexible, with draw timing |
Savers who like lottery-style upside |
| Cash ISA |
Interest-based, usually predictable |
Capital protected if provider is solvent |
Tax-free interest |
Usually quick |
People who want a known return |
| Stocks and Shares ISA |
Market-based, can rise or fall |
No capital guarantee |
Tax-free growth and gains |
Can be quick, but market value moves |
Long-term money not needed soon |
Which metric matters most
If the first question is “How much will this make?”, Premium Bonds are the weakest of the three for planning. If the first question is “Will I lose the capital?”, all three can be acceptable in different ways, but the risk shows up in different places. Premium Bonds hide the risk in the return. A Stocks and Shares ISA hides it in the value.
The mistake is to compare a headline rate with a prize fund and stop there. That is only the cover of the book. The real story sits inside the terms, the time horizon and the tax position.
If the money must pay for something on a fixed date, certainty usually beats prize potential.
Why market ISAs can beat premium bonds
A market ISA can beat Premium Bonds when the expected net return stays ahead of the prize average over the full holding period. That needs enough time, sensible charges and a portfolio that suits the saver. The point is not to chase the highest past return. The point is to ask whether the money can sit still long enough to let compounding work.
Martin Lewis often pushes people to compare products on plain facts rather than emotion. That is the right instinct here. A saver who wants a higher long-term return may need to accept some rough patches on the way. A saver who cannot tolerate a 10% drop should not pretend a market ISA is the same as cash.
After fees, net return matters
A fund charging 0.25% a year and returning 6% before fees is not the same as a fund charging 1.00% and returning 6% before fees. The charges eat the result. That is the part many people miss when they compare only the market headline.
The same logic applies to Premium Bonds. The prize fund rate is already after NS&I's structure, but it still does not tell one saver what they will earn. The useful question is simple: what is the likely cash outcome for this balance over this period?
Horizon length changes the result
Over one year, Premium Bonds can easily underperform a decent Cash ISA. Over five years, a well-matched market ISA may pull ahead if markets behave reasonably and the saver stays invested. The longer the money sits, the more the compounding effect can matter.
A case like this comes up often: someone places £20,000 in Premium Bonds because the balance feels “too big” for cash. Twelve months later, they have a few small prizes and no clear plan. A five-year ISA with modest growth could have produced a more useful result, even after a rough patch or two.
Premium Bonds are a comfort product for many savers. A market ISA is a growth product. Mixing the two in your head causes costly mistakes.
A market ISA beats Premium Bonds only when time and risk tolerance are on the saver’s side.
The point where a market ISA starts to beat Premium Bonds depends on more than headline returns. A basic-rate taxpayer with spare personal savings allowance may find a taxable savings account or a cash ISA efficient for short periods, but once the balance is large enough and the time horizon stretches beyond a year or two, the predictable savings rate from cash becomes easier to compare against the uncertain prize fund rate. Premium Bonds may still appeal if the saver values tax-free prizes and capital protected access, yet for money held five years or more, a market ISA often wins when the expected return is meaningfully above cash and the investor can tolerate volatility.
That is especially true for savers with no immediate need for withdrawals and a willingness to ride out market falls.
Common mistakes and hidden risks
The most frequent error at this point is treating Premium Bonds like a better cash account. That mindset leads to bad comparisons. It also makes savers overlook inflation, which quietly reduces what the money can buy even when the capital number stays the same.
Another common slip is assuming NS&I safety means the product must be best for every purpose. It does not. Safety, access and return are separate questions. The right answer changes depending on what the saver needs the money to do.
Big balances do not remove randomness
A balance of £50,000 gives more entries, not a guaranteed win. That feels obvious once said out loud, but plenty of people miss it when they see the account total. More tickets improve the chances only in a broad sense.
For a saver wanting regular income, that is a real problem. Premium Bonds do not pay monthly rent or tuition fees in a fixed way. A Cash ISA does. A market ISA might, if the saver sells at the right time, but that comes with market risk.
Inflation is the silent test
Inflation is the rise in prices over time. If money grows more slowly than prices, its buying power shrinks. That is the part most comparisons forget.
If a Cash ISA pays 4% and inflation runs at 3%, the real gain is only about 1% before tax complications and rate changes. Premium Bonds can look safe while still losing ground in real terms. The prize may feel exciting, yet the weekly shop still costs more next year.
Access can still trip people up
Easy access sounds simple, but the detail matters. Some accounts allow quick withdrawals, while others need a notice period or sell units at the next available price. That matters a lot if the money might be needed for repairs, bills or a house move.
NS&I's purchase and withdrawal process is straightforward, but prize timing can still cause awkward results. A saver can withdraw before a monthly draw and miss the chance of a prize. That is not a huge technical flaw, but it is a very real practical one.
Premium bonds, cash ISAs and tax-free savings
Tax-free does not mean equal. That is the short version. Premium Bonds, Cash ISAs and Stocks and Shares ISAs all sit inside tax-efficient wrappers, but each one solves a different problem.
The ISA allowance was £20,000 for the 2024/25 tax year. That is the annual limit for new ISA subscriptions across the main ISA types. Anything above that has to go elsewhere. ISA regulations are set by HM Treasury, with HM Revenue and Customs handling the tax rules that sit around them. ISA rules
Tax-free does not mean equal
A saver with modest interest income may not need an ISA just to avoid tax. A saver with larger balances, higher income or several accounts may value the wrapper more. The personal savings allowance can cover some interest, so the tax edge is not always as large as people expect.
That is why the right comparison is not “tax-free versus taxable”. It is “which tax-free wrapper matches the job?”. Premium Bonds suit people who value the chance of a prize. Cash ISAs suit people who want a known rate. Stocks and Shares ISAs suit people who can wait and accept ups and downs.
Inflation is the silent test
A product can be safe and still be poor at preserving value. That is the part many promotional pages never say clearly. Safety stops loss of capital. It does not stop loss of buying power.
Rishi Sunak and Jeremy Hunt both spent time in office during periods when savers faced higher interest rates and higher inflation, which made the comparison sharper for ordinary households. The lesson stayed the same. Look at the real return, not just the label.
Tax-free status helps most when the return itself is already strong.
Frequently asked questions
Do premium bonds count towards ISA allowance?
No, they do not. Premium Bonds sit outside the ISA allowance because they are an NS&I product, not an ISA. The £20,000 annual ISA limit applies to ISA subscriptions only. That means someone can hold Premium Bonds and also use a Cash ISA or Stocks and Shares ISA in the same tax year, subject to the product rules.
Are premium bonds better than a cash ISA for
Usually not for someone who wants a predictable return. A Cash ISA paying around 4% gives a known path, while Premium Bonds give a variable prize outcome. At £20,000, the prize average may look competitive, but one or two quiet years can still leave the saver behind a good Cash ISA.
How likely am i to win with £50,000 in premium
The balance gives more entries, but no fixed monthly win is guaranteed. With £50,000 you have 50,000 £1 entries in each draw, so the odds improve in a broad sense. The outcome still depends on the draw, and many holders with large balances still experience long gaps between meaningful prizes.
Does martin lewis recommend premium bonds?
He treats them as a valid option for some savers, not a universal best buy. His general line is to compare the expected return with cash rates and use Premium Bonds mainly when the saver wants the chance of a prize and accepts inconsistency. That view fits the numbers better than the marketing does.
Can a stocks and shares ISA beat premium bonds in
Yes, but it can also lose badly in one year. A market ISA may outperform if shares or funds rise enough after fees, yet a drop in markets can leave the saver worse off than cash. Short time frames make the outcome much less certain, so this suits money that can stay invested.
Is NS&I safer than a bank account?
It is safer in a different way, not a magic way. NS&I is backed by HM Treasury, while bank deposits are usually covered by the Financial Services Compensation Scheme up to £85,000 per eligible person, per firm. Both can be very safe, but the return story and access rules still differ.
What is the biggest mistake people make with
They treat the prize fund rate like interest. That is the main error. The better question is what the balance is likely to do over the next 12 months, 3 years or 5 years, and whether the saver can accept months with no prize at all.
This comparison does not fit people who need every pound to earn a known return, or who are trying to protect cash for a fixed date within the next few months. It also does not fit anyone who wants Premium Bonds for the thrill of a prize rather than the maths of expected value. In those cases, the choice is being made for reasons outside return comparison, and that is fine.
Which to choose now
Choose a Cash ISA if the money needs a known return, clean access and little fuss. Choose Premium Bonds if the saver accepts uneven outcomes and likes the chance of a tax-free prize. Choose a Stocks and Shares ISA if the money can stay invested for years and the saver wants growth that can outpace cash over time.
The strongest practical answer is plain: for most people comparing £5,000 to £50,000, a decent Cash ISA beats Premium Bonds on certainty, and a market ISA can beat both on long-term growth if the saver can wait. Premium Bonds only win when the prize idea itself matters enough to justify the uncertainty.
If the money has a job to do, use the product that matches the job. That usually means a Cash ISA for short-term safety and a Stocks and Shares ISA for long-term growth. Premium Bonds sit off to the side, useful for some people, but rarely the cleanest choice when the return has to work hard.
