Stable Numbers
Pension vs ISA Calculator
Enter a net monthly budget and compare how far it goes in a pension versus a Stocks and Shares ISA. Choose salary sacrifice, net pay or relief at source, add employer match, fees and growth, then see the effective uplift, final pots and a real-terms view. Includes break-even growth, share link and CSV export.
Used to label months in the schedule.
Tax and salary setup
Enter the rate that applies to extra income you defer.
Used for salary sacrifice savings.
Optional recycle below.
Applied to NI saved on salary sacrifice only.
This tool does not model carry forward.
For higher or additional rate, reduces effective net cost over time.
Employer match
Leave blank for no cap.
Growth, fees and inflation
If on relief at source and above basic rate, this treats the extra relief as money you later add to the ISA evenly through the year.
Notes: salary sacrifice saves both income tax and employee NI on the sacrificed slice, and your employer may add their NI saving. Net pay saves income tax only. Relief at source adds 20 percent at the provider then any extra rate relief is claimed later. The annual allowance and provider rules still apply. Markets can fall as well as rise.
Show monthly schedule
| # | Date | Pension start | Emp gross | ER match | ER NI | Growth | Fees % | Pension end | ISA start | ISA contrib | ISA relief | ISA growth | ISA fees % | ISA end |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Figures are nominal. Real-terms values appear in the summary.
About this calculator
Pensions are designed for retirement. Money is usually locked until the normal minimum pension age, which is scheduled to rise. ISAs are flexible and can be accessed at any time. This tool compares the two with a single constraint, your monthly net budget. It converts that budget into a pension contribution based on the relief method, applies your employer’s match and any employer NI recycling, then projects forward with growth and fees. The ISA path invests the same budget after fees and growth, with an option to add extra rate relief to the ISA when you use relief at source.
Three relief methods are supported. Salary sacrifice reduces your contractual pay and saves both income tax and employee NI on the sacrificed slice. Some employers add their NI saving to the pension. Net pay routes the contribution through payroll which reduces taxable pay, so you save income tax but still pay NI. Relief at source treats what you pay as net of basic rate tax, the provider adds 20 percent, and any extra rate relief is usually claimed later. In all cases the annual allowance and scheme rules apply.
The result cards show the effective uplift from tax relief and employer money, the final pots in nominal and real terms and the break-even ISA growth needed to match your pension under your inputs. Markets move, so treat growth as an assumption. Fees are near certain, so they matter. This is a planning tool, not advice.
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