Salary sacrifice lowers the pay that income tax and National Insurance are worked out on, because the amount you give up never counts as earnings. On £50,000 a year, sacrificing 5% of pay puts £2,500 into the pension and reduces take-home pay by £1,800.08, which is less than the amount sacrificed. Your employer's National Insurance falls too.
What salary sacrifice actually is
Salary sacrifice is a change to your contract, not a payroll setting. You agree to give up part of your salary, and your employer agrees to provide something else instead. For a pension, that something else is a larger employer contribution.
The consequence follows from the contract. Pay you have given up is never earnings, so there is nothing for income tax or National Insurance to be charged on. That is why the arrangement works, and why it cannot be applied retrospectively to pay you have already become entitled to.
Your payslip shows the reduced salary as your gross pay, and the pension contribution normally appears as an employer contribution rather than an employee one. A payslip that still shows an employee pension deduction is describing a different arrangement.
What happens to the figures
On £50,000 a year, take-home pay is £39,520.12. Sacrificing 5% of salary moves £2,500 into the pension and leaves £37,720.04 of take-home pay, a reduction of £1,800.08.
The gap between £2,500 and £1,800.08 is the income tax and National Insurance that is no longer charged on that slice of pay. How large it is depends on which rates the sacrificed slice was sitting in: a basic-rate taxpayer saves 20% of income tax and 8% of National Insurance on it, and a higher-rate taxpayer saves 40% and, above the upper earnings limit, 2%.
Your employer also stops paying employer National Insurance at 15% on the sacrificed pay. Some employers add that saving to the pension contribution and some keep it; the scheme rules say which, and it is worth knowing before comparing two employers' offers.
Against the other two methods
Put the same 5% contribution through each of the three routes and the pension receives £2,500 every time. What differs is your pay. Under a net pay arrangement, £50,000 leaves £37,520.12 of take-home pay; under relief at source, £37,520.12; under sacrifice, £37,720.04.
The reason sacrifice sits highest is National Insurance. The other two methods change what is deducted from your pay, so income tax moves and National Insurance does not. Sacrifice changes the pay itself, so both move, and that difference is what shows up in the take-home figure.
Comparing methods on take-home pay alone is still incomplete. The three questions that matter together are what reaches the pension, what reaches your bank, and what the employer contributes, because some employers add their own National Insurance saving to the pot and some do not.
The things it changes that are not tax
Statutory payments are worked out from average weekly earnings, and sacrificed pay is not earnings. Statutory maternity, paternity, shared parental and sick pay can all be lower as a result, and the effect lasts for as long as the relevant reference period.
Borrowing is assessed on the salary a lender can see. A mortgage offer based on gross pay is based on the reduced figure, though many lenders will consider the pre-sacrifice salary if you ask.
Cover and entitlements that are multiples of salary, such as death-in-service benefits and some redundancy formulas, may be calculated on the reduced figure unless the scheme says otherwise.
And the State Pension depends on National Insurance record, which is credited by earnings above the lower earnings limit. A sacrifice that takes earnings below that point breaks the qualifying year; one that leaves earnings well above it does not.
The floor it cannot go through
A sacrifice cannot take your pay below the National Minimum Wage or National Living Wage for the hours you work. From 1 April 2026 the rate for workers aged 21 and over is £12.71 an hour, and the pay used for that test is the pay after the sacrifice.
That is why employers cap the percentage for lower-paid staff, and why a sacrifice arrangement can stop working after a change in hours rather than a change in pay.
A percentage of what?
Schemes differ in what the percentage is applied to, and the difference is larger than the percentage itself. Some use your full pay. Some use qualifying earnings, which for 2026/27 means the band between £6,240 and £50,270. Some use basic pay only, excluding overtime and bonuses.
Two employers both offering the same headline percentage can therefore be paying quite different amounts into a pension. The scheme documents say which definition applies, and it is the first thing to read when comparing offers.
The cap announced for 2029
A limit on the National Insurance advantage has been announced. From 6 April 2029, the amount of pension contributions that can be sacrificed free of National Insurance is to be capped at £2,000 a year, with sacrifice above that treated as earnings for National Insurance.
The measure is recorded in our rules file as announced rather than in force, with its source. Nothing on this page applies it to a figure for 2026/27, and it will reach the calculations on the day it takes effect rather than being written into the text now.
Can I stop or change a sacrifice?
It is a contractual change, so it is changed by agreement with your employer rather than by asking payroll. Most arrangements allow changes at set points in the year, and most allow an earlier change on a life event such as a birth, a redundancy in the household or a marriage.
Because the change is contractual, it applies to pay you have not yet earned. It cannot be unwound for months that have already been paid.
Whether it is right for you
This guide explains what the arrangement does to each figure. Whether it suits your circumstances depends on your age, your other savings, your borrowing plans, the benefits you rely on and the scheme your employer offers, and none of that is visible to a calculation.
For advice on your own position, a regulated financial adviser is the person to ask. MoneyHelper, the government-backed guidance service, is a free starting point.