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ISA vs SIPP Calculator

Which wrapper is right for your retirement savings?

The SIPP's tax relief advantage is powerful, but the ISA's flexibility and tax-free drawdown matter too. This calculator shows the true after-tax comparison based on your situation.

This calculator provides information and guidance only. It does not constitute regulated financial advice under the Financial Services and Markets Act 2000. Outputs are illustrative and based on current assumptions — they are not a prediction of future returns or outcomes. Tax rules, allowances, and legislation may change. Please consult a regulated financial adviser before making significant financial decisions.

What does it actually cost you? (per year)

ISA

£6,000

from take-home pay

SIPP

£4,800

for the same £6,000 gross

£1,200 saved per year by using SIPP — that's 20% effective tax relief

How your SIPP contribution works

You pay out of pocket£6,000
Provider adds at source (20% basic-rate relief)+£1,500
Total invested in your SIPP pot£7,500

Both ISA and SIPP cost £6,000 from your take-home pay per year. The SIPP pot receives more because of tax relief.

SIPP wins

SIPP is better by £17,898

For the same annual cost to you, the SIPP pot grows larger thanks to 20% tax relief

Side-by-side comparison

MetricISASIPP
Gross invested per year£6,000£7,500
Net cost to you per year£6,000£6,000
Tax relief rateNone20%
Projected pot at 65£286,363£357,953
Est. tax on drawdown£0£53,693
Net after-tax value£286,363£304,260

Your tax relief rate

20%

Added at source by pension provider

Annual SIPP saving

£1,200

vs contributing to ISA

Important caveats

  • • SIPP minimum access age is 57 from 2028 (currently 55). ISA money is always accessible.
  • • Employer contributions are only available via SIPP/workplace pension — a significant SIPP advantage not shown here.
  • • The ISA annual allowance is £20,000 for 2026/27. The SIPP annual allowance is £60,000 (or 100% of earnings if lower).
  • • If your retirement income stays within the Personal Allowance (£12,570), SIPP drawdown is tax-free.
  • • The 25% Pension Commencement Lump Sum (PCLS) is always tax-free, regardless of your marginal rate.
  • • Salary sacrifice (if available from your employer) would also save National Insurance contributions — toggle the option above to see the difference.

Portfolio growth over time (same gross contribution)

Read our detailed ISA vs SIPP article

Your details

Used to calculate your marginal tax rate

Gross amount — the pension adds tax relief on top

Applied to 75% of SIPP withdrawals

Annual return before fees, nominal

Enable to model employer salary sacrifice (also saves NI)

Scottish income tax rates

Applies to residents of Scotland only

Want a complete retirement projection?

For a complete retirement projection including tax, State Pension, and 10,000 Monte Carlo simulations — use our full retirement planner.

Open retirement planner

This calculator provides estimates for guidance only. Results are illustrative and do not constitute financial advice. Always verify figures with a qualified adviser.