Cash ISA vs Stocks and Shares ISA: a practical comparison
By calculatemysalary.co.uk Editorial Team
Cash ISAs protect your money. Stocks and Shares ISAs grow it (usually). How to decide which one to use, or whether to split your £20,000 allowance between both.
The ISA allowance for 2025/26 is £20,000. Every penny of growth inside an ISA — whether interest, dividends, or capital gains — is tax-free. The question is where to put it.
Cash ISA: your money stays put
A Cash ISA works like a savings account. You deposit money, it earns interest, and HMRC doesn't touch it. Your capital is protected by the Financial Services Compensation Scheme up to £85,000 per institution.
Current easy-access rates sit around 3–5% depending on the provider. Fixed-rate deals pay a bit more if you lock your money away for a year or two.
Good for: emergency funds, money you need within 1–3 years, anyone who can't stomach the idea of their savings dropping in value.
Watch out for: introductory "bonus" rates that halve after 12 months, fixed-term accounts with early withdrawal penalties, and inflation risk. If inflation is 4% and your ISA pays 3%, your money is quietly losing purchasing power even though the number in your account goes up.
Stocks and Shares ISA: your money goes to work
A Stocks and Shares ISA lets you invest in funds, individual shares, bonds, and other assets inside a tax-free wrapper. Historically, global stock markets have returned around 7–10% per year on average over long periods. But "on average" is doing a lot of heavy lifting in that sentence. Individual years can be brutal.
You'll pay platform fees (typically 0.15–0.45% per year) and fund charges (0.10–1.00% depending on whether you pick index trackers or actively managed funds).
Good for: money you won't need for at least five years, long-term goals like retirement or a house deposit that's years away, anyone comfortable with short-term drops for long-term growth.
Watch out for: investments can fall in value and you might get back less than you put in. Fees compound over time. And you need the discipline not to panic-sell when markets dip 15% on a bad Tuesday.
Comparison
| Cash ISA | Stocks & Shares ISA | |
|---|---|---|
| Risk | Very low | Medium to high |
| Typical returns | 3–5% (current rates) | 7–10% long-term average (highly variable) |
| Can you lose money? | No (FSCS protected up to £85k) | Yes |
| Access | Usually instant | Usually a few working days |
| Fees | None or minimal | Platform + fund fees |
| Tax treatment | Interest is tax-free | Dividends and gains are tax-free |
| Best time horizon | 1–3 years | 5+ years |
A practical split
You don't have to pick one. Many people split their allowance. A common approach:
- £5,000 in a Cash ISA as an emergency buffer — roughly three months of essential spending, accessible immediately
- £15,000 in a Stocks and Shares ISA invested in low-cost index funds for long-term growth
The right split depends on your situation. If you already have a solid emergency fund in a regular savings account, you might invest the full £20,000. If you're saving for a wedding next year, cash is the obvious choice.
Do you even need a Cash ISA?
Basic rate taxpayers get £1,000 of savings interest tax-free through the Personal Savings Allowance (£500 for higher rate taxpayers). If your savings are small enough that your interest stays under this threshold, a Cash ISA gives you no extra tax benefit over a normal savings account — and normal accounts sometimes pay better rates.
The ISA advantage kicks in when your savings are large enough that you'd otherwise pay tax on the interest, or when you want to shelter future growth from tax as your pot grows over the years.
Costs matter more than you think
Say you invest £10,000 in a Stocks and Shares ISA for 20 years at an average 7% annual return.
- With 0.2% total fees: you'd end up with roughly £36,200
- With 1.0% total fees: roughly £29,500
That 0.8% difference in annual fees costs you about £6,700 over two decades. Index tracker funds from providers like Vanguard or Fidelity typically charge 0.10–0.25%. Actively managed funds charge more and rarely outperform consistently enough to justify the premium.
Which ISA should you pick?
Choose a Cash ISA if you need the money soon, you can't afford any loss of capital, or you don't yet have an emergency fund.
Choose a Stocks and Shares ISA if you're investing for five years or more and you can tolerate watching your balance drop by 20% without selling.
Use both if you want safety for short-term money and growth for long-term money. There's no bonus for simplicity here — splitting your allowance is fine.
Use our salary calculator to see how much you have left after tax each month. That's your starting point for working out how much you can save.