- Cash ISA — pays interest, no risk to capital, FSCS-protected up to £85,000. Best for goals under 5 years.
- Stocks & Shares ISA — invests in markets, can lose value short-term, historically beats cash over 10+ years.
- Both share the £20,000 annual allowance. You can split it however you like.
- The longer your time horizon, the more it pays to lean toward stocks. Under 5 years, cash. Over 10 years, mostly stocks. In between, a mix.
What is an ISA?
An Individual Savings Account is a UK tax wrapper, not a single product. Anything inside an ISA — interest, dividends, capital gains — is completely free of UK income tax and capital gains tax. You don't even have to declare it on a self-assessment return.
The catch: you can only put in £20,000 each tax year (6 April to 5 April), and unused allowance doesn't roll over. This makes it less about choosing between Cash and Stocks & Shares and more about choosing the right mix.
See the difference over time
Illustration only. Cash ISA assumed at % AER. Stocks & Shares ISA assumed at % nominal annual return before fees, in line with long-run global equity averages. Past performance doesn't guarantee future results. Capital at risk for stocks. Try the full savings calculator for inflation-adjusted figures.
Cash ISA — the safe option
A Cash ISA is a savings account inside an ISA wrapper. You deposit money, it earns interest, and that interest is tax-free. There are three main types:
- Easy-access Cash ISA — withdraw anytime. Variable rate, currently up to about 4.85% AER from top providers.
- Fixed-rate Cash ISA — locked away for 1 to 5 years. Higher rate (up to ~5.00% AER for a 1-year fix), but penalties for early access.
- Notice Cash ISA — somewhere in between: give 30, 60 or 90 days' notice to withdraw, slightly better rate than easy-access.
Your money is protected up to £85,000 per banking licence by the FSCS — the UK government-backed deposit guarantee. If the bank fails, you get it back.
The downside: with UK inflation hovering around 2–3%, a 4.5% Cash ISA gives you roughly 1.5–2.5% above inflation in real terms. Reasonable, but not transformational.
Stocks & Shares ISA — the long-term option
A Stocks & Shares ISA invests your money in markets — shares of companies, government bonds, corporate bonds, or (most commonly) low-cost index funds that hold a basket of all of these. The value goes up and down, sometimes sharply, but historically over 10+ year periods a globally diversified portfolio has returned roughly 5–7% above inflation.
That's the headline. The reality is messier:
- Annual returns vary wildly. A typical year might be +10%, but losses of 20–30% in a single year are not rare.
- The "average return" only works over long periods. Picking a 12-month window in 2008 or early 2020 would have shown a big loss.
- Costs matter. Pay 0.25% in platform fees plus 0.20% in fund fees and you're losing nearly half a percent a year — compounded over decades, that's significant.
For most people, a Stocks & Shares ISA invested in a single globally diversified, low-cost index fund (typical fee 0.10–0.25%) gets you the bulk of the benefit with minimum complexity.
Side-by-side comparison
| Feature | Cash ISA | Stocks & Shares ISA |
|---|---|---|
| Typical return (real, after inflation) | 0% to +2% | +4% to +7% over the long run |
| Risk to capital | None (FSCS protected) | Can lose 20–30%+ short-term |
| Liquidity | Easy-access: instant. Fixed: locked. | Sell takes 2–5 business days |
| Best for | Emergency fund, short-term goals (1–5 years) | Long-term goals (10+ years) |
| Fees | None typically | 0.10–0.45% platform + 0.05–0.25% fund |
| FSCS protection | £85,000 of deposit | £85,000 of provider failure (not market loss) |
How to choose — the time-horizon rule
The single most useful filter is your time horizon — how long until you need the money.
- Under 3 years (deposit for a house, big purchase, emergency fund) — Cash ISA. Markets can crash and not recover in time.
- 3 to 7 years — Mostly Cash, with maybe 20–30% in Stocks. A balanced approach.
- 7 to 15 years — Mostly Stocks & Shares, with a small cash buffer. The historical odds of beating cash over 10 years are strongly in your favour.
- Over 15 years (retirement, kids' uni fees in 18 years) — Stocks & Shares ISA, almost certainly. The "rule of 72" says money invested at 7% doubles every ~10 years.
Splitting your £20,000 allowance
Since April 2024, you can pay into multiple ISAs of the same type within a single tax year — so opening a new Cash ISA mid-year doesn't lock out your existing one. You can also split your £20,000 across types freely:
- Up to £20,000 in any combination of Cash ISA + Stocks & Shares ISA + Innovative Finance ISA
- Of that £20,000, up to £4,000 can go into a Lifetime ISA (which gets a 25% government bonus but locks the money until first-home purchase or age 60)
A common pattern: an emergency fund of 3–6 months' expenses in a Cash ISA, then surplus going into a Stocks & Shares ISA for long-term growth. Once your cash buffer is big enough, redirect 100% of new contributions to the Stocks & Shares ISA.
Common mistakes
- Withdrawing and re-depositing — this counts as a new contribution against your annual allowance. Always use a formal ISA transfer form when moving money between providers.
- Panic-selling in a market downturn — locks in losses you'd otherwise have ridden out. Stocks & Shares ISAs work because of long-term compounding, which requires staying invested.
- Not using your full allowance — £20,000 a year is a "use it or lose it" benefit. If you're saving anywhere outside an ISA while having allowance left, you're paying unnecessary tax.
- Picking individual shares — fun, occasionally lucrative, statistically a losing strategy for most people. A boring global index fund usually beats a clever stock-picking strategy after 5–10 years.
- Choosing a high-fee platform — 0.45% sounds tiny but it can compound into tens of thousands lost over 30 years. The cheapest options charge 0.15–0.25%.
Where to open one
Cash ISAs are available from most UK banks, building societies and challenger banks. Top easy-access and fixed rates are usually offered by smaller providers competing on rate. Compare top Cash ISA rates on our deals page — refreshed regularly.
Stocks & Shares ISAs are offered by investment platforms. Look for low platform fees (under 0.25%), a good selection of low-cost index funds, and clear pricing.
Frequently asked questions
What's the difference between a Cash ISA and a Stocks & Shares ISA?
A Cash ISA pays interest like a savings account, with FSCS protection up to £85,000 and zero risk to your capital. A Stocks & Shares ISA invests in shares, funds and bonds — your money can grow much faster over time but can also fall in value. Both shelter returns from UK income tax and capital gains tax.
Can I have both a Cash ISA and a Stocks & Shares ISA?
Yes. You can split your £20,000 annual allowance across different ISA types in any proportion. Since April 2024 you can also pay into multiple ISAs of the same type in the same tax year.
How much can I put in an ISA in 2026/27?
£20,000 across all ISA types combined. The Lifetime ISA portion is capped at £4,000 of that total. The allowance resets each tax year on 6 April.
Are ISAs really tax-free?
Yes — interest, dividends and capital gains inside an ISA are completely free of UK tax, and you don't need to declare them on a self-assessment return.
Can I lose money in a Stocks & Shares ISA?
Yes — the value of investments can fall as well as rise. Over short periods losses are common; over 10+ years a diversified portfolio has historically delivered positive real returns. The FCA-regulated platform is protected by FSCS, but the investments themselves are not guaranteed.
Should I transfer my Cash ISA to a Stocks & Shares ISA?
If the money is for long-term goals (10+ years) and you can tolerate volatility, transferring some or all is worth considering. Always use a formal ISA transfer (not withdrawal + new deposit) so you keep the tax-free wrapper.
Is a Cash ISA better than a regular savings account?
Only if you'd otherwise pay tax on the interest. Basic-rate taxpayers get a £1,000 personal savings allowance and higher-rate taxpayers get £500 — interest above that is taxed. If your savings income exceeds those allowances, a Cash ISA shelters everything. If it doesn't, a non-ISA savings account often pays a slightly higher rate.
Related guides
How UK income tax works in 2026/27
Understand the tax you're avoiding by using an ISA.
Salary sacrifice: is it worth it? 2026/27
A pension pays in pre-tax; an ISA pays out tax-free. When to use which.
UK stamp duty 2026/27: SDLT, LBTT & LTT
Saving for a first home? A LISA can fund the deposit — but check the rules.
Full Savings & ISA Calculator
Compound interest with inflation-adjusted real value.
Disclaimer: This article is for illustrative and educational purposes only and is not financial, tax or investment advice. The value of investments can fall as well as rise and you may get back less than you invested. Past performance does not guarantee future results. For personalised advice please consult an FCA-authorised financial adviser.