How pension contributions actually flow
A £100 pension contribution doesn't simply leave your bank account and arrive in your pension as £100. It interacts with the payroll calculation in one of three ways, each producing a different take-home outcome:
| Mechanism | Income Tax saving | NI saving | What appears on payslip |
|---|---|---|---|
| Salary sacrifice | Yes — at marginal rate, automatic | Yes — 8% or 2% | Reduced gross + employer contribution |
| Net pay arrangement | Yes — at marginal rate, automatic | No | Pension line above NI deduction |
| Relief at source | 20% automatic; higher-rate via Self Assessment | No | Pension line below NI deduction |
Most modern UK workplace pensions use relief at source. Many older occupational schemes (especially in the public sector) use net pay arrangement. Salary sacrifice is increasingly common in tech and financial services.
Worked examples — £30,000 salary, 5% contribution
Take a £30,000 rUK earner in 2026/27. Without any pension contribution, their take-home is about £25,120. A 5% contribution (£1,500/year, £125/month) plays out differently depending on the mechanism:
Salary sacrifice (5% sacrifice)
- Gross pay reduced from £30,000 to £28,500
- Income Tax: £3,186 (vs £3,486 without sacrifice = £300 saved)
- NI: £1,274 (vs £1,394 = £120 saved)
- Take-home: £24,040 (vs £25,120 = £1,080 reduction)
- Pension contribution: £1,500
- Effective cost: £1,080 take-home for £1,500 in pension
Net pay arrangement (5% contribution)
- Gross pay still £30,000 for NI; £28,500 for Income Tax
- Income Tax: £3,186 (£300 saved)
- NI: £1,394 (no saving)
- Take-home: £23,920 (vs £25,120 = £1,200 reduction)
- Pension contribution: £1,500
- Effective cost: £1,200 take-home for £1,500 in pension
Relief at source (5% contribution — based on stated gross of £1,500)
- Gross pay: £30,000
- Income Tax: £3,486 (no payroll change)
- NI: £1,394 (no change)
- You pay £1,200 from net pay
- Provider adds £300 basic-rate relief from HMRC
- Effective cost: £1,200 take-home for £1,500 in pension
For a basic-rate taxpayer, salary sacrifice saves £120 more per year than the other two methods (the NI difference). Across a working career, this compounds meaningfully.
Worked examples — £50,000 salary, 8% contribution
At £50,000 (rUK, just below the higher-rate threshold), a more substantial 8% contribution (£4,000/year):
Salary sacrifice (8%)
- Gross reduced from £50,000 to £46,000
- Income Tax: £6,686 (vs £7,486 = £800 saved)
- NI: £2,674 (vs £2,994 = £320 saved)
- Take-home: £36,640 (vs £39,520 = £2,880 reduction)
- Pension contribution: £4,000
- Effective cost: £2,880 take-home for £4,000 in pension
Relief at source (8% based on gross of £4,000)
- Gross: £50,000
- Income Tax: £7,486 (no payroll change)
- NI: £2,994 (no change)
- You pay £3,200 from net pay
- Provider adds £800 basic-rate relief
- Effective cost: £3,200 take-home for £4,000 in pension
The £320 difference between methods at this salary level reflects the NI savings under salary sacrifice. For someone right at the higher-rate threshold, the choice of mechanism is meaningful.
Worked examples — £75,000 salary, higher-rate territory
At £75,000, you're a higher-rate taxpayer with a 42% marginal rate above £50,270. A 10% pension contribution (£7,500/year):
Salary sacrifice (10%)
- Gross reduced from £75,000 to £67,500
- Income Tax: £14,432 (vs £17,432 = £3,000 saved — much higher because of higher-rate relief)
- NI: £3,361 (vs £3,511 = £150 saved)
- Take-home: £49,707 (vs £54,057 = £4,350 reduction)
- Pension contribution: £7,500
- Effective cost: £4,350 take-home for £7,500 in pension (58% effective cost)
Relief at source (10%)
- Gross: £75,000
- Income Tax: £17,432 (no payroll change)
- NI: £3,511 (no change)
- You pay £6,000 from net pay
- Provider adds £1,500 basic-rate relief (£7,500 gross)
- You claim £1,500 higher-rate relief via Self Assessment (or tax code adjustment)
- Effective net cost after the extra claim: £4,500 take-home for £7,500 in pension (60% effective cost)
For higher-rate taxpayers, salary sacrifice is meaningfully more efficient — and administratively simpler because the full relief is automatic.
The £100k taper effect
The most dramatic effect is in the £100,000-£125,140 personal allowance taper band. At £105,000, the marginal rate is 62%. A £5,000 salary sacrifice:
- Income Tax saved at 40% on the £5,000: £2,000
- Income Tax saved on the £2,500 of restored personal allowance: £1,000
- NI saved at 2%: £100
- Total tax/NI saved: £3,100
- Pension contribution: £5,000
- Effective cost: £1,900 take-home for £5,000 in pension (38% effective cost)
This is why salary sacrifice is so attractive for earners in this band — every £1 sacrificed costs only 38p of take-home.
Cumulative effect over a career
A 30-year-old contributing 5% via salary sacrifice on a £35,000 salary that grows 3% a year, with the contributions invested at 5% annual return, would accumulate approximately:
- Total contributions over 37 years (to age 67): about £105,000
- Total take-home cost (after tax/NI savings): about £75,000
- Estimated pot at age 67: about £200,000
These figures use approximate UK long-term assumptions. The Pension Projection Calculator models specific scenarios — different contribution rates, return assumptions, employer match, salary growth, and time horizons.
Choosing a contribution rate
Common starting points (not advice — choices vary widely by individual circumstance):
- The match cap — if your employer matches up to N%, contributing at least N% captures all available employer money
- 5% — the auto-enrolment statutory minimum for employees
- 10% — a commonly-cited "comfortable retirement on average earnings" rate
- 15%+ — typical for higher earners or those starting pension saving later
The "right" rate depends on your age, income, other savings, retirement age target, and risk tolerance — questions a calculator can model but only personal financial advice can answer for your situation.
When more isn't more
A few scenarios where stopping at lower contributions makes sense:
- Near the State Pension qualifying threshold — sacrificing below £6,396 of earnings risks losing a qualifying year
- Mortgage in flight — see the trade-offs in is salary sacrifice worth it?
- Approaching the £60,000 annual allowance — contributions above attract the annual allowance charge
For most workers in their working years, increasing pension contributions improves long-term financial position even at the cost of current take-home. The trade-off is concrete: today vs decades from now.