Salary sacrifice vs net-pay vs relief-at-source — which one actually wins?

Three pipes, one pension pot

UK workplace pensions can route your contribution to the same pot through three structurally different pipes: salary sacrifice, net pay arrangement, and relief at source. They all eventually deposit money in the same Master Trust or contract-based plan — but the journey through the payroll engine determines whether you save National Insurance, whether you get higher-rate tax relief automatically, and how much pension you actually end up with per £1 of take-home pay foregone.

Most employees never see the mechanism on their payslip; they see a line like "Pension: £150" deducted and that's it. The difference between the three mechanisms can be hundreds of pounds a year on a modest contribution and thousands a year on a six-figure salary. This guide unpacks each one, runs the numbers, and tells you what to do if your employer's default isn't the best fit.

1. Salary sacrifice — agreed before pay-day

Under salary sacrifice you sign a contractual variation with your employer: your gross salary drops by the agreed contribution, and your employer pays the equivalent amount directly into your pension. From HMRC's perspective, the sacrificed slice was never your earnings — so neither income tax nor NI is computed on it.

What you save

• Income tax at your marginal rate (20%, 40% or 45% in rUK; 19%, 20%, 21%, 42%, 45% or 48% in Scotland).
• Employee NI at 8% (between PT and UEL) or 2% (above UEL).
• Employer NI at 15%, saved by your employer. Many UK schemes contractually pass that 15% saving into your pension pot — read your scheme T&Cs to be sure.

The headline number that gets quoted at this point is "every £1 of net pay foregone becomes £1.50–£1.80 of pension". For a basic-rate taxpayer that's roughly right; for a higher-rate taxpayer it's closer to £1.70; in the £100k taper zone it can be over £3.00 per £1 foregone.

What you give up

• Borrowing capacity. Mortgage affordability is assessed on gross — sacrificed gross. Some lenders add back the sacrifice but the policy varies. If you're 6–12 months from a mortgage application, run the sacrifice past your broker first.
• State benefits and statutory pay. Statutory Sick Pay, Maternity Pay, Adoption Pay etc. are calculated on post-sacrifice earnings. A 5% sacrifice modestly reduces them; a 30% sacrifice in the run-up to maternity leave can be a real hit.
• Floor at NMW. Sacrifice can never push your effective earnings below the National Minimum / Living Wage for your contracted hours. The employer is legally responsible for stopping you before that happens.
• The £2,000 NIC exemption cap from April 2029. Sacrifices above this annual figure will retain income-tax relief but lose the employee-NI saving on the excess. See the compliance notice in the Salary Sacrifice Optimiser.

2. Net pay arrangement — the occupational default

"Net pay" is a confusing name because the contribution doesn't come from net pay — it comes from gross, but after NI. The pension contribution is deducted from your gross before income tax is computed, so you get income-tax relief automatically at your full marginal rate. National Insurance is still calculated on the original full gross, so you do not get NI relief.

What you save

• Income tax at your full marginal rate — identical to salary sacrifice.

What you don't save

• Employee NI. You're still paying 8% (or 2% above UEL) on the contribution.
• Employer NI. Your employer pays full 15% Secondary Class 1 on your full gross, so they have no NI saving to pass through.

Net pay was historically problematic for very low earners — if your gross was below the PA, you got no tax relief at all because there was no income tax to relieve. HMRC introduced a "top-up" payment from 2024/25 to fix that, but it lags contributions by about a year.

3. Relief at source — workplace personal pensions

Common in stakeholder pensions, Group Personal Pensions and most employer-arranged "personal pension" products. The contribution is deducted from your net pay (i.e. after income tax and NI). The pension provider then claims a 20% top-up from HMRC and credits it to your pot, so a £80 net contribution becomes a £100 pension credit.

What you save

• Basic-rate tax (20%) — automatically, via the provider's reclaim from HMRC.

What you have to chase

• Higher-rate tax (the extra 20p above the basic 20p) and additional-rate tax (the extra 25p) must be claimed back through Self-Assessment — or via a one-off written request to HMRC if you don't file a return.
• NI relief — you don't get any.

Higher-rate taxpayers using relief-at-source schemes who don't file Self-Assessment routinely under-claim their full relief. HMRC estimates run in the high hundreds of millions per year of unclaimed higher-rate pension relief. The relief is yours; it just doesn't arrive unless you ask for it.

Side-by-side, £100 contribution

Assumptions: 40% income-tax bracket, NI 2% (upper rate), employer passes their 15% NI saving into your pension under sacrifice. £100 of total pension credit either way.

The salary-sacrifice row assumes the employer passes the £15 NI saving into your pot. If they don't, sacrifice still beats net pay by exactly the £2 of NI you save personally.

The Scottish footnote

Scottish income-tax rates differ from rUK across six bands. NI stays UK-wide. The salary-sacrifice advantage is identical in magnitude — but at the band edges (£43,663 and £100,000) the leverage is enormously higher because Scottish marginals run to 50%, 67.5%, and 69.5%. See Scotland's 67.5% tax trap for the math.

Under relief-at-source schemes the pension provider always reclaims at the rUK basic rate of 20%, even for Scottish basic-rate taxpayers (whose rate is 20%) or starter-rate (19%). HMRC reconciles the 1p difference annually. For higher / advanced / top-rate Scottish taxpayers, the extra slab still has to be claimed via Self-Assessment — exactly the same problem as in rUK.

How to find out which one you have

1. Look at your latest payslip. Is the pension deduction before the line that says "Gross taxable pay"? That's salary sacrifice.
2. Is the deduction between "Gross pay" and "Taxable pay" but after the NI line? That's net pay arrangement.
3. Is the pension deduction taken from after-tax net pay (typically named "Pension PP" or similar)? That's relief at source.

If you can't tell, ask payroll. The question to use is "is my workplace pension administered under salary sacrifice, net pay arrangement, or relief at source?". They will know.

Practical decision tree

• Employer offers salary sacrifice and passes the employer-NI saving into your pension: use it. No comparable alternative for most UK earners.
• Salary sacrifice available but employer keeps the NI saving: still preferable for the employee NI alone, unless mortgage / maternity considerations dominate.
• Only net pay or relief at source available, you're a higher- or additional-rate taxpayer: pick whichever your employer operates and file Self-Assessment to claim the extra relief if you're on RAS.
• Only net pay available, you're a basic-rate taxpayer: it's essentially identical to sacrifice for the income-tax slice, so no extra action required.

Model your own contribution

The Salary Sacrifice Optimiser shows the exact net-pay drop, tax saved, NI saved and employer NI saved for any £-amount or %-of-gross sacrifice — including the 60% / 67.5% trap rescue button when your income crosses £100,000. Type your gross in, drag the sacrifice up, and read the leverage ratio at the bottom of the True Cost panel.