How Does Salary Sacrifice Work? NI Savings, Tax Benefits & Pitfalls

Salary sacrifice (also called salary exchange) is a formal agreement to reduce your gross salary in exchange for your employer paying more into your pension. Because the sacrifice happens before tax and National Insurance are calculated, both you and your employer pay less NI.

The maths

Say you sacrifice an extra £1,000 into your pension:

Income tax saved: £200 (basic rate)
Employee NI saved: £80 (8%)
Net cost to you: £720 for £1,000 in pension
Employer NI saved: £150 (15% from April 2025)

Many employers pass their NI saving back into your pension, making it even better value.

Potential drawbacks

Mortgage affordability: lenders use your reduced salary, which may lower borrowing capacity
State benefits: some benefits are linked to earnings; sacrificing too much could affect entitlement
Life assurance: if death-in-service is a multiple of salary, your reduced salary means a lower payout

Why it beats an ordinary pension contribution

A normal workplace contribution under net pay or relief at source gets you income tax relief, but National Insurance is still calculated on your full salary first. Salary sacrifice removes the money before both, so you avoid income tax and employee NI together.

For a basic rate taxpayer that difference is 8% of the amount sacrificed. For someone earning between roughly £50,270 and £60,000 it can be considerably more, because sacrificing can pull taxable income back below the higher rate threshold and, for parents, back under the High Income Child Benefit Charge.

Worked comparison at £1,000

Ordinary contribution: £1,000 gross into the pension costs £800 from net pay after basic rate relief. NI has already been paid on the full amount.
Salary sacrifice: the same £1,000 into the pension costs £720 from net pay, because 20% income tax and 8% employee NI are both avoided.
Difference: £80 per £1,000, or 8%, purely from the NI treatment.

If your employer passes on its own NI saving, the pension receives £1,150 rather than £1,000 for that same £720 of net pay, which is a materially better outcome again.

The higher rate and £100,000 cliff edges

Salary sacrifice is at its most valuable around two thresholds. Just above the higher rate threshold, sacrificing the excess converts income taxed at 40% plus 2% NI into pension contributions, which is an unusually efficient trade.

Above £100,000 the personal allowance is withdrawn at £1 for every £2 of income, producing an effective marginal rate of around 60% on the band between £100,000 and £125,140. Sacrificing income back below £100,000 restores the allowance and is one of the few straightforward ways to escape that band.

The National Minimum Wage floor

You cannot sacrifice salary below the National Minimum Wage for your hours. This is a hard legal limit rather than a scheme rule, and it means lower earners often cannot sacrifice as much as the arithmetic would otherwise suggest. Employers are required to police it, which is why some schemes cap the percentage available.

What you give up

Beyond the mortgage and death-in-service points above, two smaller effects are worth knowing. Statutory payments such as maternity and paternity pay are calculated from post-sacrifice earnings, so a sacrifice running through the qualifying period can reduce them. And because sacrifice is a contractual variation rather than a payroll instruction, it usually cannot be switched off on demand, only at scheme-defined points or on a qualifying life event such as a birth, marriage or redundancy.

None of these make sacrifice a bad idea for most people. They are simply the reasons to check your own position rather than assume the general case applies.

Work out your own numbers

Calculate your exact NI saving with our salary sacrifice calculator, see the employer side with the employer NI saving calculator, or read how this interacts with borrowing in our mortgage impact guide.

General information, not financial advice. Rates and thresholds change between tax years. Consider regulated advice before making significant changes to your pension arrangements.