ISA Returns on £20,000

Investing £20,000 in a UK ISA at 4.5% earns £4,924 tax-free over 5 years and £11,059 over 10 years. A basic rate taxpayer saves £20 in tax over 5 years compared to a standard savings account.

With £20,000 in an ISA at 4.5%, you earn £4,924 tax-free over 5 years. Outside an ISA, a basic rate taxpayer would pay £20 in tax on the same returns, while a higher rate taxpayer pays £937. Over 10 years, the ISA advantage grows to £243 (basic rate) or £2,245 (higher rate) in tax saved.

ISA returns on £20,000 over time

The table below shows how £20,000 grows in an ISA at 4.5% versus a taxable account, for a basic rate (20%) and higher rate (40%) taxpayer.

Period	ISA value	ISA return	Non-ISA return (basic)	Tax saved (basic)	Tax saved (higher)
1 year	£20,900	£900	£900	£0	£160
3 years	£22,823	£2,823	£2,823	£0	£520
5 years	£24,924	£4,924	£4,903	£20	£937
10 years	£31,059	£11,059	£10,795	£243	£2,245

Returns assume compound growth at 4.5% per year. Non-ISA accounts deduct tax annually on interest above the PSA.

How the interest rate affects your ISA advantage

Higher rates mean more interest, more tax, and a bigger ISA advantage. Here is how £20,000 performs over 5 years at different rates (basic rate taxpayer):

Rate	ISA return	Non-ISA return	Tax saved
3.0%	£3,185	£3,185	£0
4.5%	£4,924	£4,903	£20
6.0%	£6,765	£6,384	£346
8.0%	£9,387	£8,410	£852

How to invest £20,000 in an ISA

£20,000 fits within the annual £20,000 ISA allowance, so you can invest the full amount in a single tax year. You have several options:

• Cash ISA — Fixed or easy-access savings accounts. Currently paying 4–5%. Best for money you may need within 1–3 years.
• Stocks & Shares ISA — Invest in funds, ETFs, or individual shares. Higher potential returns over 5+ years, but your capital is at risk.
• Split approach — Keep an emergency fund (3–6 months' expenses) in a Cash ISA and invest the rest in a Stocks & Shares ISA for long-term growth.

If you are aged 18–39 and saving for a first home or retirement, consider a Lifetime ISA (LISA): you get a 25% government bonus on contributions up to £4,000/year (£1,000 free per year). The LISA counts toward your £20,000 annual ISA allowance.

Compare ISA returns at other amounts

• £15,000: £3,693 tax-free over 5 years (£0 tax saved)
• £18,000: £4,431 tax-free over 5 years (£0 tax saved)
• £22,000: £5,416 tax-free over 5 years (£84 tax saved)
• £25,000: £6,155 tax-free over 5 years (£228 tax saved)

Frequently asked questions

How much will £20,000 earn in an ISA?

At 4.5%, £20,000 earns £4,924 tax-free over 5 years, growing to £24,924. Over 10 years, it grows to £31,059 (£11,059 return).

How much tax do I save with an ISA on £20,000?

Over 5 years at 4.5%, a basic rate taxpayer saves £20 and a higher rate taxpayer saves £937. Over 10 years, savings increase to £243 (basic) and £2,245 (higher).

Cash ISA or Stocks & Shares ISA?

Cash ISAs are lower risk and suit savings you may need within 1–3 years. Stocks & Shares ISAs have higher potential returns over 5+ years but your capital is at risk. Many people use both — cash for near-term needs and investments for long-term growth.