How to use the calculator
The calculator takes 5 inputs:
- Annual gross salary — your contractual gross pay
- Pension sacrifice % — the percentage you want to sacrifice into pension
- Region — England/Wales/NI or Scotland (different bands)
- Tax year — 2026/27 or 2025/26
- Student loan plan (optional) — if you have one, tick it
Output sections:
- Tax + NI saved — the headline figure showing your total saving from sacrifice
- Side-by-side breakdown — your position without vs with sacrifice across Income Tax, NI, student loan, and net take-home
- Cost per £100 to pension — the most useful single figure: how much take-home it costs you to put £100 into pension
Reading the outputs
Tax + NI saved (annual)
The combined Income Tax + employee NI saving from sacrificing. For a higher-rate earner sacrificing £5,000, expect roughly £2,100 saved. For basic rate, roughly £1,400.
Cost per £100 to pension
The most actionable output. Shows your "effective cost" of contributing — what £100 in pension actually costs you in take-home.
| Marginal rate | Cost per £100 to pension |
|---|---|
| Basic rate (28%) | £72 |
| Higher rate (42%) | £58 |
| Allowance taper (62%) | £38 |
| Additional rate (47%) | £53 |
So if the calculator shows £58 per £100, you're a higher-rate taxpayer. If it shows £38, you're in the £100k allowance taper — where pension sacrifice is most valuable.
Side-by-side breakdown
Compares all major deductions before and after sacrifice. The "Income Tax" line drops; the "National Insurance" line drops; the "Pension contribution" appears as a new line; the "Net take-home" drops by less than the gross sacrifice because of the tax savings.
Worked example — basic-rate earner
£35,000 salary, 5% sacrifice (£1,750 to pension):
- Without sacrifice: net annual ~£28,720
- With sacrifice: net annual ~£27,720
- Take-home reduction: £1,000
- Pension contribution: £1,750
- Tax + NI saved: £750
- Cost per £100 to pension: £57
Wait — that's lower than the headline 72p for basic rate. Why? The £1,750 sacrifice pushes a slice of income below the basic-rate threshold; on that slice the marginal rate is the personal allowance + NI = 8%. The calculator handles the band-by-band split automatically.
Worked example — higher-rate earner
£75,000 salary, 8% sacrifice (£6,000 to pension):
- Without sacrifice: net annual ~£54,057
- With sacrifice: net annual ~£50,577
- Take-home reduction: £3,480
- Pension contribution: £6,000
- Tax + NI saved: £2,520
- Cost per £100 to pension: £58
A £6,000 pension contribution at a £3,480 take-home cost. The £2,520 saved is the higher-rate tax + NI relief that would otherwise have gone to HMRC.
Worked example — £100k taper earner
£115,000 salary, 13% sacrifice (£14,950 to pension):
The sacrifice keeps total income exactly at £100,050 — out of the allowance taper.
- Without sacrifice: net annual ~£71,000 (with allowance taper costing thousands)
- With sacrifice: net annual ~£65,250
- Pension contribution: £14,950
- Tax + NI saved: £8,650
- Cost per £100 to pension: £38 (the 60% effective marginal rate saving)
For workers between £100,000 and £125,140, sacrifice is exceptionally tax-efficient — every £100 to pension costs only £38 of take-home.
When to use the calculator
Common use cases:
- Negotiating a pay rise above £100k — calculate how much to sacrifice to stay out of the taper
- Considering a bonus — sacrifice the bonus into pension before payment
- Checking auto-enrolment opt-up — see the take-home impact of increasing from default 5%
- Planning around a benefit change — assessing impact of company car removal etc.
What the calculator doesn't model
- Long-term pension growth (use the pension projection calculator)
- Future tax-rate changes
- Pension annual allowance breach (you must respect the £60,000 cap manually)
- Tapered annual allowance specifics if total income > £260,000
- State Pension qualifying years (NI history)
For these, see the broader pension cluster.
Verifying the figures
To sanity-check the calculator's output for your situation:
- Open the take-home pay calculator
- Calculate your take-home with 0% pension
- Recalculate with the same % sacrifice
- The difference in take-home should match the salary sacrifice calculator's "take-home reduction"
The two calculators use the same UKTax engine so figures should align exactly.
In short
The salary sacrifice calculator turns abstract "20% / 40% / 60%" tax-relief percentages into concrete £ figures for your specific salary. The "cost per £100 to pension" output is the single most useful number — if it's £58, you're a higher-rate taxpayer. If it's £38, you're in the £100k taper. For broader context see Is salary sacrifice worth it? → and Salary sacrifice explained →.