Decision Tool

ISA vs Pension: which wins for you?

The most common UK personal finance dilemma — with no universal answer. Enter your details and see which wrapper generates more after-tax wealth given your specific situation.

Educational only. This is a simplified model. Real outcomes depend on future tax rates, investment returns, and rule changes. Not financial advice.

Your situation

Stocks & Shares ISA
£0
after-tax accessible wealth
Pension (SIPP / Workplace)
£0
after-tax accessible wealth
Calculating...

How the comparison works

The key variables that determine which wins are: your current tax rate (pension gets relief going in), your retirement tax rate (ISA is tax-free coming out), the length of time invested (both compound equally inside), and whether you have an employer match (which always tips the scales toward pension).

✅ Pension wins when...
You're a higher rate taxpayer now
Employer match is available
You expect lower taxes in retirement
Time horizon is 10+ years
Salary sacrifice reduces your NI too
📦 ISA wins when...
You're a basic rate taxpayer now AND in retirement
No employer match available
You may need the money before age 57
Simplicity and flexibility matter most
You're already maximising employer match

The rule of thumb hierarchy

  1. Always maximise the employer pension match first. This is a 100% immediate return on the matched portion. Nothing else comes close.
  2. If you're a higher rate taxpayer, pension contributions next. Each £1 contributed costs you only 60p (40% relief). The ISA cannot match this.
  3. Use ISA for flexibility and medium-term goals. No locked-in age, no drawdown rules, completely accessible. Ideal for FIRE aspirations or goals before 57.
  4. If you're a basic rate taxpayer with no employer match, the ISA and pension are broadly equivalent in many scenarios — choose based on when you need the money.
  5. Both, if you can. The optimal strategy for most people is pension first (for the tax relief and employer match) then ISA for the remainder of investable income.
⚠️ The pension lock-in you must factor in

Pension money is inaccessible until age 57 (rising from 55 in 2028). If there is any realistic chance you need the money before then — career break, house purchase, emergency fund — the ISA's flexibility has a genuine value that this model cannot fully quantify. Never put money into a pension you might need within the decade.

Official References
gov.uk — Tax relief on pension contributions explained gov.uk — ISA allowances and rules MoneyHelper — Pension vs ISA: which is better?