ISA Returns on £15,000

Investing £15,000 in a UK ISA at 4.5% earns £3,693 tax-free over 5 years and £8,295 over 10 years. A basic rate taxpayer saves £0 in tax over 5 years compared to a standard savings account.

With £15,000 in an ISA at 4.5%, you earn £3,693 tax-free over 5 years. Outside an ISA, a basic rate taxpayer would pay £0 in tax on the same returns, while a higher rate taxpayer pays £462. Over 10 years, the ISA advantage grows to £1 (basic rate) or £1,227 (higher rate) in tax saved.

ISA returns on £15,000 over time

The table below shows how £15,000 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	£15,675	£675	£675	£0	£70
3 years	£17,117	£2,117	£2,117	£0	£243
5 years	£18,693	£3,693	£3,693	£0	£462
10 years	£23,295	£8,295	£8,294	£1	£1,227

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 £15,000 performs over 5 years at different rates (basic rate taxpayer):

Rate	ISA return	Non-ISA return	Tax saved
3.0%	£2,389	£2,389	£0
4.5%	£3,693	£3,693	£0
6.0%	£5,073	£5,029	£44
8.0%	£7,040	£6,591	£398

How to invest £15,000 in an ISA

£15,000 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

• £10,000: £2,462 tax-free over 5 years (£0 tax saved)
• £13,000: £3,200 tax-free over 5 years (£0 tax saved)
• £17,000: £4,185 tax-free over 5 years (£0 tax saved)
• £20,000: £4,924 tax-free over 5 years (£20 tax saved)

Frequently asked questions

How much will £15,000 earn in an ISA?

At 4.5%, £15,000 earns £3,693 tax-free over 5 years, growing to £18,693. Over 10 years, it grows to £23,295 (£8,295 return).

How much tax do I save with an ISA on £15,000?

Over 5 years at 4.5%, a basic rate taxpayer saves £0 and a higher rate taxpayer saves £462. Over 10 years, savings increase to £1 (basic) and £1,227 (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.