True side-by-side comparison after all taxes, charges and relief. The answer depends on your rates now — and in retirement.
ISA — tax-free growth & incomePension — upfront tax relief
Your Situation
£
£
yrs
%
£
How this works
For ISA: you invest after-tax money, it grows tax-free, and all withdrawals are tax-free. For pension: you invest pre-tax money (upfront relief), it grows tax-free, then 25% of withdrawals are tax-free and 75% are taxed at your retirement rate. The calculator uses your salary to determine your current tax rate automatically.
After-Tax Retirement Income Comparison
Stocks & Shares ISA
—
annual tax-free income
Amount invested (post-tax)—
Pot at retirement—
Total contributed (nominal)—
Income in retirement—
Tax on withdrawals£0 (tax-free)
Pension (Relief at Source)
—
annual after-tax income
Amount invested (pre-tax gross)—
Pot at retirement—
25% tax-free lump sum—
Taxable income (75% of pot)—
Tax on withdrawal—
Sensitivity: Tax Rate Now vs. In Retirement
The key insight
Pension wins when your current tax rate is HIGHER than your retirement tax rate (relief claimed at 40%, tax paid at 20%). ISA wins when you expect the same or higher tax rate in retirement, or when you want complete flexibility and certainty.
Current Tax Rate
Retirement Rate
ISA Net Income
Pension Net Income
Winner
Advantage
When Pension wins
Higher-rate taxpayers (40%+) who expect to pay basic rate (20%) in retirement gain a 20% tax advantage on contributions. Salary sacrifice adds an additional 8% NI saving. For a 40% taxpayer, a £100 salary sacrifice costs just £52 in take-home pay (vs £80 in an ISA).
When ISA wins
If you expect to pay higher-rate tax in retirement (large pension drawdown), or you want flexibility to access funds at any age (no minimum pension access age restriction), or you want absolute certainty on withdrawals being tax-free. ISA contributions also don't count toward the pension annual allowance (£60,000/year).
25% tax-free lump sum (PCLS)
You can take up to 25% of your pension pot tax-free (capped at £268,275 from 2024/25). This calculator models a sustainable drawdown strategy where the TFLS is retained to offset tax. The optimal strategy often combines both: max pension for the tax relief, then ISA for flexibility once pension is funded.
ISA vs Pension — the complete UK guide
Both ISAs and pensions allow investments to grow tax-free, but they differ in when you receive the tax benefit. With a pension, the government tops up contributions with tax relief (20% basic rate, 40% higher rate), making it more efficient upfront. However, withdrawals in retirement are taxed as income (except the 25% tax-free lump sum, capped at £268,275).
With a Stocks and Shares ISA, contributions come from post-tax income — no upfront relief — but all growth and withdrawals are completely tax-free forever. This makes ISAs especially valuable for those who expect to pay the same or higher tax rate in retirement.
The optimal UK strategy for most higher-rate taxpayers is typically: maximise pension contributions first (up to the £60,000 annual allowance) to capture the 40% relief, then use any remaining surplus in a Stocks and Shares ISA for flexibility and tax diversification in retirement.