ISA vs Pension Savings Calculator
Compare a simplified Stocks and Shares ISA path with a pension path using monthly contributions, assumed growth and a pension uplift. This fills the UK comparison gap without pretending tax rules are simple.
How to read this comparison
Related UK and retirement pages
FAQ
Is an ISA or pension better?
It depends on tax treatment, flexibility needs, retirement age, employer contributions and future withdrawal rules.
Why include a pension uplift?
The uplift is a simplified way to model tax relief or employer contribution support.
Does this model pension tax on withdrawal?
No. Keep this page as a first-pass comparison, not personal tax advice.
The structural difference, before any numbers
An ISA and a pension are both tax wrappers around the same underlying investments. What differs is when the tax is applied and when you can reach the money. Everything else follows from those two points.
| Stocks and shares ISA | Workplace or personal pension | |
|---|---|---|
| Contributions | From money already taxed | Tax relief added at your marginal rate |
| Growth | Free of UK income and capital gains tax | Free of UK income and capital gains tax |
| Withdrawals | Tax free | Typically 25% tax free, the rest taxed as income |
| Access | Any time | From the minimum pension age, not before |
| Employer contributions | None | Often available — and usually the largest single advantage |
General structure only. Allowances, the minimum pension age and relief rules change; confirm current figures with HMRC or your provider.
Where an employer matches pension contributions, that match is an immediate return on your money before any investment growth — commonly 50% or 100%. No ISA advantage comes close. The conventional order is therefore: contribute enough to capture the full match first, then compare what to do with anything beyond it.
How the tax timing plays out over 25 years
A simplified illustration, deliberately excluding employer contributions so the wrapper effect is visible on its own. Assume £100 of gross salary, a basic-rate taxpayer paying 20% now and 20% in retirement, and 7% growth for 25 years.
| ISA route | Pension route | |
|---|---|---|
| Gross salary | £100 | £100 |
| Tax paid on the way in | £20 | £0 |
| Amount actually invested | £80 | £100 |
| Value after 25 years at 7% | £458 | £573 |
| Tax on the way out | £0 | about £86 (25% tax free, rest at 20%) |
| Left to spend | £458 | £487 |
On these assumptions the pension finishes ahead, because relief lets a larger sum compound from the start and a quarter of it comes out untaxed. The result flips if your retirement tax rate is higher than your rate today, and it flips decisively if you need the money before the minimum pension age — a pension you cannot access is worth nothing to a problem you have now.
- Higher-rate now, basic-rate later: the pension advantage widens considerably.
- Basic-rate now, higher-rate later: the ISA can win.
- Money needed before pension age: the ISA wins regardless of the tax arithmetic.
- Employer match on offer: the pension wins on that portion by a margin nothing else matches.
Questions about ISAs and pensions
Is an ISA or a pension better?
For long-term retirement money with an employer match, the pension almost always. For money you may need before pension age, the ISA. Many people sensibly use both, for different purposes.
Can I have both an ISA and a pension?
Yes, subject to each having its own annual allowance. Using both is common: the pension for retirement, the ISA for goals that arrive sooner.
What if I need the money before retirement?
Then the ISA is the right wrapper. Pension access is restricted until the minimum pension age, and no tax advantage compensates for money you cannot reach when you need it.
Does this comparison include employer contributions?
The illustration above deliberately excludes them, to isolate the tax effect. Including a match strengthens the pension side substantially — it is a return on your contribution before any market growth.