Money.Holdings
L4

Compliance Level 4: Financial Projection

Forward-looking estimates with assumptions

ISA Growth Calculator

See how much tax you save by growing your savings inside a tax-free ISA versus a taxable account.

£
£

Annual allowance: £20,000.00

20 years
%
%
Tax Saved by Using an ISA
£104,527.85
ISA Final Value
£795,890.21
Taxable Account Value
£691,362.36
Total Contributions
£405,000.00

What if you kept going for 5 more years?

+£90,702.30 tax saved

Important Disclaimer

This calculator provides estimates for educational purposes only. Results are based on the inputs you provide and standard financial formulas. They do not constitute financial, investment, tax, or legal advice. Consult a qualified professional before making financial decisions.

Frequently Asked Questions

The annual ISA allowance is £20,000.00 for the 2025/26 tax year. You can split this across different types of ISA (cash, stocks & shares, etc.), but the combined total can't exceed the allowance.

Tax on gains and dividends compounds negatively the same way growth compounds positively — a small annual tax drag erodes an increasing amount of value each year as your balance grows, which is why the gap between an ISA and a taxable account widens over long time horizons.

Not necessarily — the UK has separate tax-free allowances for dividends and capital gains outside an ISA too, though they've shrunk substantially in recent years. High-balance, long-term investors are the ones who benefit most from ISA tax-free growth.

Yes — the annual allowance doesn't roll over. Unused allowance from this tax year is gone once the new tax year starts on 6 April.

Sources & References

  1. Individual Savings Accounts (ISAs)GOV.UK (2025)

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Important Disclaimer

This calculator provides estimates for educational purposes only. Results are based on the inputs you provide and standard financial formulas. They do not constitute financial, investment, tax, or legal advice. Consult a qualified professional before making financial decisions.