ISAs — The UK Tax Wrapper You Must Use

£20,000 a year, all gains tax-free — not using this is leaving money on the table

7 min read Beginner

"A Stocks and Shares ISA lets you invest up to £20,000 per year with zero capital gains tax and zero dividend tax on anything inside it. If you are a UK investor not using one, you are paying tax you do not have to pay."

For educational purposes only. Nothing in this chapter is financial advice. All figures are illustrative examples. Tax rules, account types, contribution limits, and regulations differ by country and change over time. Always verify current rules with official government sources or a qualified financial adviser before making any investment decisions.

What an ISA Is

An ISA (Individual Savings Account) is a tax wrapper — an account that sits around your investments and makes all gains and income inside it tax-free. You do not pay capital gains tax when you sell. You do not pay income tax on dividends. You do not pay interest tax on cash savings. The investments inside are identical to any other account; it is the tax treatment that is different.

ISA types in 2024/25

Cash ISA

£20,000 allowance

Savings accounts with tax-free interest

Stocks and Shares ISA

£20,000 allowance

Shares, ETFs, funds, bonds — investments

Lifetime ISA (LISA)

£4,000/year (within £20k limit)

First home purchase or retirement — 25% government bonus

Junior ISA

£9,000 allowance (separate)

For under-18s — accessible at 18

Key Rules to Know

£20,000 annual allowance

You can deposit up to £20,000 per tax year (April 6 to April 5) across all ISAs combined. Unused allowance does not roll over — use it or lose it.

One of each type per year

You can open and pay into one Stocks & Shares ISA and one Cash ISA per tax year, but not two of the same type.

Transfers do not use allowance

Moving money between ISA providers (ISA transfer) does not count against your annual allowance and preserves the tax-free status.

No annual reporting

Unlike general investment accounts, you do not need to declare ISA gains or income on your self-assessment tax return.

How Much the Tax Saving Is Worth

Capital gains tax outside an ISA: 18% (basic rate) or 24% (higher rate) on investment gains above the £3,000 annual exemption (2024/25). Dividend tax above £500: 8.75% (basic) or 33.75% (higher). Inside an ISA: zero on both.

On a £100,000 portfolio generating 4% dividends per year, a higher-rate taxpayer outside an ISA pays approximately £1,183/year in dividend tax alone. Over 20 years, that is over £23,000 — before accounting for the compounding those payments would have generated.

The Lifetime ISA — Worth It?

The LISA pays a 25% government bonus on contributions up to £4,000/year — a maximum of £1,000 free money annually. But there are restrictions: you can only use the money penalty-free for a first home purchase (under £450,000) or retirement (age 60+). Withdrawal for any other reason incurs a 25% penalty — which effectively takes back the bonus and a slice of your own money.

FAQs

Can I have an ISA and a SIPP?

Yes. ISA and SIPP allowances are completely separate. A SIPP gives upfront tax relief on contributions. An ISA gives tax-free growth and withdrawal. Most financial planners recommend maximising both.

Can I invest in US stocks inside a UK ISA?

Yes. Most UK brokers allow US-listed shares and ETFs inside an ISA. Note: US-listed ETFs may have 15% withholding tax on dividends that cannot be reclaimed inside an ISA.

What happens to my ISA if I die?

Your ISA passes to your estate. Your spouse or civil partner can inherit your ISA allowance (Additional Permitted Subscription) without it counting against their own allowance.

Is the ISA allowance going up?

The £20,000 limit has been unchanged since 2017/18. There is no confirmed increase as of 2024/25. Always verify current limits at gov.uk.

Key takeaways

An ISA is a tax wrapper — all gains, dividends, and interest inside are completely tax-free.
£20,000 annual allowance (2024/25) — use it or lose it, no rollover.
Stocks and Shares ISA: the primary vehicle for long-term UK investment.
Lifetime ISA: 25% government bonus, but restricted to first home or retirement use.
ISAs and SIPPs are separate allowances — you can and should consider using both.