Why employment income matters for retirement modelling
In brief: If you are still working — or expect to work part-time in early retirement — your employment income is the starting point for everything else in your projection. It determines how much you can save, how much tax you pay alongside other income sources, and when you can afford to stop.
Most people approaching retirement are in one of two positions: winding down a career and trying to work out how their final working years feed into retirement, or already partially retired and combining part-time work with pension income. Either way, understanding how employment income is taxed — and how it interacts with pension drawdown, State Pension, and other income — is essential for getting the projection right.
Gross pay vs net pay
Your payslip shows the journey from gross salary to net take-home. The main statutory deductions are:
- Income tax — collected by your employer via the PAYE (Pay As You Earn) system
- National Insurance (Employee Class 1) — a separate deduction for social insurance
Other deductions may include pension contributions, student loan repayments, childcare vouchers, and any voluntary deductions (share schemes, cycle to work, etc.).
Gross salary is the starting point for income tax and NI calculations, and also the figure used for many other purposes: mortgage affordability assessments, life insurance multiples, and some state benefit calculations.
Income tax on employment (PAYE)
Employment income is subject to income tax, collected via the PAYE (Pay As You Earn) system. Your employer deducts tax from each pay packet based on the tax code HMRC issues for you, and pays it directly to HMRC on your behalf.
How your tax code works
Your tax code tells your employer how much tax-free income to allow before deducting tax. The most common code is 1257L (2025/26 and 2026/27), which corresponds to the standard Personal Allowance of £12,570. The letter indicates how the allowance is applied (L = standard allowance, subject to normal rules).
Adjustments to your tax code can reflect:
- Untaxed income (rental income, freelance work) — reduces the code
- Benefits in kind (company car, private medical insurance) — reduces the code
- Underpaid tax from previous years — reduces the code
- Additional allowances (blind person’s allowance) — increases the code
If HMRC issues the wrong code, you may pay too much or too little tax during the year. Overpayments are refunded; underpayments are usually collected via the following year’s code or through Self Assessment.
Emergency tax codes
If you start a new job without providing a P45, your employer may operate an emergency tax code (suffix W1 or M1, meaning “week 1 / month 1”). Emergency codes treat each pay period in isolation — they do not account for personal allowance used earlier in the year — which can result in too much tax being deducted. This is corrected when HMRC issues the correct code.
How employment income stacks with retirement income
In the years around retirement, your employment income does not exist in isolation. A part-time salary or consultancy income is added to pension drawdown, State Pension, rental income, and anything else you receive — and the combined total determines which tax bands apply. This stacking effect means that even modest employment income, on top of other sources, can push you into a higher tax band than you might expect.
National Insurance
National Insurance (NI) is a separate system of contributions that funds the State Pension and certain contributory benefits. It is not income tax, but it functions like a payroll deduction and is collected via PAYE.
Employee Class 1 contributions (2026/27)
| Earnings band | Employee NI rate |
|---|---|
| Below £12,570 (Lower Earnings Limit equivalent) | 0% |
| £12,570 to £50,270 | 8% |
| Above £50,270 | 2% |
Employee NI applies to earnings in each pay period. Unlike income tax, NI does not consider annual income — it is assessed week by week or month by month.
Employer Class 1 contributions
Your employer also pays NI on your earnings, but this does not appear on your payslip — it is a cost to the employer above and beyond your gross salary. The employer rate is 15% on earnings above the Secondary Threshold (£5,000 per year).
This employer NI cost makes salary sacrifice (described below) attractive to employers as well as employees.
What NI pays for
NI contributions are the mechanism by which you build entitlement to the State Pension and certain contributory benefits (Jobseeker’s Allowance, Employment and Support Allowance, Maternity/Paternity Pay). You need 35 qualifying years for the full new State Pension. A year is qualifying if your earnings are above the Lower Earnings Limit (£6,396 in 2026/27).
You stop paying employee NI when you reach State Pension age, even if you continue working.
Brief historical note: contracting out
Before April 2016, some employees were “contracted out” of the additional State Pension in exchange for reduced NI contributions (and lower State Pension entitlement). This system is now closed, but anyone with a contracted-out history will have a lower State Pension entitlement, which will be reflected in their State Pension forecast.
Salary sacrifice
Salary sacrifice (also called salary exchange) is an arrangement where you agree to give up a portion of your gross salary in exchange for a non-cash benefit — most commonly employer pension contributions.
How it works
Instead of receiving £50,000 in salary, you agree with your employer to sacrifice £5,000. Your contractual gross salary becomes £45,000. Your employer contributes the £5,000 directly into your pension.
Tax and NI savings
Because your gross salary has reduced, you pay less income tax and less National Insurance on the sacrificed amount. Your employer also pays less employer NI.
For a basic rate taxpayer sacrificing £5,000:
- Income tax saving: £5,000 × 20% = £1,000
- Employee NI saving: £5,000 × 8% = £400
- Total employee saving: £1,400
- Employer NI saving: £5,000 × 15% = £750 (employer benefit, sometimes passed on to employee as additional pension contribution)
The total saving of £1,400 means a £5,000 pension contribution has an effective net cost of £3,600 — compared to contributing £4,000 from net pay and claiming basic rate relief (which only returns the tax, not the NI).
Worked example
| Without sacrifice | With sacrifice | |
|---|---|---|
| Gross salary | £50,000 | £45,000 |
| Employee pension contribution | £5,000 (net) | £0 |
| Gross salary after pension | £50,000 | £45,000 |
| Income tax (approx.) | £7,486 | £6,486 |
| Employee NI (approx.) | £2,994 | £2,594 |
| Net take-home | ~£34,520 | ~£35,920 |
| Pension funded | £4,000 (after relief) | £5,000 (employer contribution) |
The salary sacrifice route puts more into the pension for the same net cost.
Important side effects of salary sacrifice
Salary sacrifice reduces your contractual gross salary, which can affect:
- Mortgage affordability — lenders assess affordability based on actual contractual salary. A reduced gross salary may lower the maximum mortgage available.
- Statutory Maternity/Paternity Pay — statutory payments are based on average weekly earnings, which are derived from actual salary. Reduced salary means lower statutory pay.
- Life cover / death in service — if your employer provides life cover as a multiple of salary (e.g., 4× salary), salary sacrifice reduces the insured amount.
- State Pension — your NI record is still credited based on the full original salary, provided your post-sacrifice salary remains above the Lower Earnings Limit. This is because pension contributions made via salary sacrifice are treated as employer contributions, and HMRC has confirmed the NI record is protected.
Pension auto-enrolment
All employers must automatically enrol eligible workers into a qualifying workplace pension. The minimum contribution under auto-enrolment is:
- 5% employee contribution (including 1% tax relief from the government)
- 3% employer contribution
- Total: 8% of qualifying earnings
Qualifying earnings for auto-enrolment are earnings between £6,240 and £50,270 per year (2026/27). Contributions are calculated on this band, not total earnings. Some employers use a different definition of pensionable pay, which can result in higher effective contributions.
You have the right to opt out of auto-enrolment, but your employer must re-enrol you every 3 years. Opting out permanently requires active action every 3 years. If you opt out, you lose the employer contribution — effectively declining a portion of your total remuneration.
Working in retirement
Many people continue earning in some capacity after they begin drawing a pension — part-time employment, consultancy, or freelance work. This is increasingly common, and the tax treatment is straightforward: the income is taxed exactly like any other employment income, stacked on top of your other sources for the year.
The complication is in the interaction. If you are drawing pension income and earning a salary in the same year, the combined total determines your tax band. A £20,000 part-time salary on its own sits comfortably in the basic rate band. The same salary on top of £15,000 of pension drawdown and £12,548 of State Pension puts your total at £47,548 — still basic rate, but with very little headroom before higher rate tax begins.
There is also a specific pension trap to be aware of. Once you start flexibly accessing a defined contribution pension (taking taxable income from drawdown or UFPLS), the Money Purchase Annual Allowance (MPAA) is triggered. This permanently reduces the annual limit for future pension contributions from £60,000 to £10,000. Salary sacrifice pension contributions count as money purchase contributions — so if you are working in retirement and still sacrificing salary into a pension while also drawing from another pension, the MPAA may limit how much you can contribute.
These projections are for modelling purposes only. They do not constitute financial advice. Tax rules are subject to change. Please consult a qualified financial adviser before making financial decisions.