Cash ISA vs stocks & shares ISA
Same £20,000 allowance, same tax-free wrapper — but two very different jobs. One keeps your money safe and steady; the other puts it to work in the market. The right answer comes down almost entirely to one thing: when you’ll need the money.
The verdict
It hinges on your time horizon. For money you’ll need within roughly one to five years — an emergency fund, a house deposit, a near-term goal — a cash ISA is the sensible home: capital-protected, predictable, tax-free interest. For money you can leave untouched for five years or more, a stocks & shares ISA has historically grown far more, and the tax-free wrapper compounds that advantage. They’re not rivals so much as tools for different jobs — and you can hold both.
Cash ISA
Tax-free interest on savings
- Capital protected — can’t fall in value
- Predictable, guaranteed interest rate
- Interest tax-free, beyond any PSA limit
- Returns often trail inflation long-term
- No real growth potential
- Cash allowance shrinking from 2027
Stocks & shares ISA
Tax-free investing in the market
- Higher long-term growth potential
- Growth, dividends & gains all tax-free
- Beats inflation over long periods
- Value can fall as well as rise
- Best left untouched 5+ years
- No guaranteed return
Both are tax-free — so what’s the real difference?
Start with what they share, because it’s the source of the confusion. Both sit inside the same £20,000 annual ISA allowance, and inside both, your returns are entirely free of UK tax. The difference is purely in how those returns are made. A cash ISA earns interest — steady, predictable, and your balance never drops. A stocks & shares ISA invests in assets like funds and shares, so its value moves with the market: up over the long run, historically, but with real dips along the way.
That single distinction is the whole decision. It’s not “which is better” in the abstract — it’s “which suits this particular pot of money.” And the deciding factor is time. Over one year, the gap between a cash ISA and a stocks & shares ISA is small and the market’s volatility isn’t worth the risk. Over twenty years, that gap becomes enormous, and the volatility smooths out into a long upward trend. The catch worth knowing: the same money in the same wrappers produces wildly different outcomes depending only on how long you leave it.
£20,000 over time: the horizon effect
Here’s the same £20,000 lump sum in each wrapper, at illustrative rates of 4.5% for cash and 7% for investments. These aren’t predictions — investment returns vary and can be negative — but they show why time changes everything.
| Held for | Cash ISA (~4.5%) | S&S ISA (~7%) | Difference |
|---|---|---|---|
| 1 year | £20,900 | £21,400 | £500 |
| 5 years | £24,924 | £28,051 | £3,127 |
| 10 years | £31,059 | £39,343 | £8,284 |
| 20 years | £48,234 | £77,394 | £29,159 |
Read down the right-hand column: at one year the investment edge barely covers a nice dinner; at twenty years it’s larger than the original sum. That’s compounding doing its work — and it’s exactly why a stocks & shares ISA only makes sense for money you genuinely won’t touch. Pull it out during a market dip in year two and you could crystallise a loss the cash ISA would never have shown.
When each one wins
Cash ISA wins when…
- You’ll need the money within 1–5 years.
- It’s your emergency fund or a house deposit.
- You can’t risk the balance falling at all.
- You’re a higher-rate taxpayer with savings above the £500 PSA.
Stocks & shares ISA wins when…
- You can leave the money invested for 5+ years.
- You’re building long-term wealth or retirement savings.
- You can tolerate the value rising and falling.
- You want growth that has historically beaten inflation.
Two things worth knowing before you choose. First, you don’t have to pick one — since 2024 you can pay into both a cash ISA and a stocks & shares ISA in the same tax year, as long as your combined contributions stay within £20,000. Many people sensibly do exactly that: cash for the near-term safety net, investments for the long game. Second, a change is coming. From April 2027, savers under 65 will be able to put a maximum of £12,000 of their allowance into cash ISAs, with the rest reserved for investments — so if cash is your preference, the rules are tightening.
Common questions
Is a cash ISA or stocks and shares ISA better?
It depends on your time horizon. For money you’ll need within one to five years, a cash ISA is usually better — it’s capital-protected and predictable. For money you can leave for five years or more, a stocks and shares ISA has historically grown significantly more, despite short-term ups and downs. They serve different jobs, and you can hold both within your £20,000 allowance.
Can I have both a cash ISA and a stocks and shares ISA?
Yes. Since April 2024 you can pay into multiple ISAs of different types in the same tax year, provided your total contributions don’t exceed the £20,000 annual allowance. A common approach is to use a cash ISA for short-term savings and an emergency fund, and a stocks and shares ISA for long-term growth.
How much is the ISA allowance?
The annual ISA allowance is £20,000 for the 2026/27 tax year, shared across all ISA types you hold. It resets each 6 April and can’t be carried forward — unused allowance is lost. From April 2027, savers under 65 will be limited to £12,000 of that allowance in cash ISAs, with the remainder for stocks and shares or other ISAs.
Does a stocks and shares ISA really beat cash over time?
Historically, over long periods, yes — though it’s never guaranteed. On illustrative figures, £20,000 might grow to around £48,000 in a cash ISA over 20 years but roughly £77,000 in a stocks and shares ISA. The investment advantage builds with time through compounding, which is why it suits money left untouched for five years or more, not short-term savings.
Why might a higher-rate taxpayer prefer a cash ISA for savings?
Because a higher-rate taxpayer’s Personal Savings Allowance is just £500 — interest above that is taxed at 40% in a normal savings account. A cash ISA shelters all interest from tax regardless of the amount, overriding the PSA limit entirely. For higher earners holding significant cash, that makes the cash ISA wrapper genuinely valuable, not just a box-ticking choice.
What’s changing with cash ISAs in 2027?
From 6 April 2027, savers under 65 will be able to deposit a maximum of £12,000 per tax year into cash ISAs, with the balance of the £20,000 allowance reserved for stocks and shares or other ISAs. Those aged 65 and over keep the full £20,000 cash allowance. If you favour cash, it’s worth factoring this tightening into longer-term plans.
Related tools & guides
How we put this together
Comparison reflects current UK ISA rules: a £20,000 annual allowance for 2026/27 shared across ISA types, tax-free returns in both, and the ability since 2024 to pay into multiple ISA types in one tax year. From April 2027, under-65s face a £12,000 cash ISA limit within the overall allowance.
Growth figures use illustrative rates of 4.5% for cash and 7% for investments, compounded annually, and cross-checked. These are not forecasts — cash rates vary and investment values can fall as well as rise. The higher-rate Personal Savings Allowance is £500.
We review this comparison when the ISA allowance, cash ISA rules or savings allowances change.