Tax on a Second Job in the UK: How It Actually Works

Why There's No Personal Allowance on a Second Job

Every UK taxpayer gets one Personal Allowance of £12,570 per year (2025/26). It doesn't matter how many jobs you have — you can only use it once.

When you take a second job, HMRC has no way of knowing (initially) how your allowance is already being used by your first employer. The default response is to assign your second job a tax code with no free pay — meaning tax is deducted from pound one.

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The Tax Codes HMRC Assigns

BR is by far the most common second-job code for people earning under £50,270 in their main job.

Can the PA be split between two jobs?

Yes — you can ask HMRC to split your Personal Allowance between two employers (e.g., allocate £7,000 to your main job and £5,570 to your second job). This only makes sense if your main job income is already lower than your PA and you don't expect the combined income to push you into a higher band. Contact HMRC via your Personal Tax Account or call 0300 200 3300.

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What You Actually Take Home: Worked Examples

Example 1: £30,000 main job + £8,000 second job

*NI on main job: (£30,000 − £12,570) × 8% = £1,394. **If second-job earnings are £8,000 and the Primary Threshold is £12,570/year, NI is £0 on the second job (under PT). However, if paid at a higher rate or the £8k exceeds what remains of the PT after main job use, this varies — NI is calculated per job per period.

Effective total tax + NI rate: ~£6,480 / £38,000 = 17.1% — not as bad as it feels because the BR code deduction is the right rate anyway.

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Example 2: £48,000 main job + £5,000 second job

Here the second job pushes total income to £53,000 — across both the basic and higher-rate bands.

In this case, D0 overcharges slightly because not all of the £5,000 second-job income falls above £50,270. The excess (£730 deducted, £270 overpaid) would be refunded via P800 after year end.

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National Insurance Across Two Jobs

NI is calculated per employment, per pay period — not on your combined annual income.

What this means in practice:

• If you earn £15,000 in job A and £6,000 in job B, you pay NI on both (above the per-job Primary Threshold of £12,570/year = £242/week).
• However, there is a maximum NI you can pay in a year. If the combined deductions exceed the annual maximum (applied to income above ~£50,270 at 8%), you're entitled to a refund of the excess employee NI.
• Employer NI is always due on each job above £5,000/year — employers cannot share or offset their NI liability.

When do you overpay NI?

If your second job pays earnings above the Primary Threshold (£242/week, £1,048/month, £12,570/year), NI is deducted at 8% from pound one above that threshold in each job. If your combined NI-able earnings are higher than if you had one combined salary, you may pay marginally more in NI.

The NI overpayment refund process: claim via your Self Assessment return, or contact HMRC after the tax year ends.

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The Self Assessment Question

You may need to file a Self Assessment return if:

• Your total income from all sources exceeds £100,000
• You have untaxed income (self-employment, rental) alongside your PAYE jobs
• HMRC has not applied the correct codes and your total tax is wrong

If both jobs are PAYE and your codes are correct, HMRC handles the reconciliation automatically via the P800 process — no Self Assessment needed.

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Common Issues (and How to Fix Them)

"My second job put me on an emergency code (1257L W1/M1), not BR"

If you provided your P45 from a previous job to your new second-job employer before having the jobs concurrently, they may have applied 1257L W1/M1. This gives you a monthly free-pay allocation that means less tax deducted — but it's wrong if your main job is already using your PA. Fix: Contact HMRC or your employer to update the code to BR.

"I think I'm on BR but my income should only be 20% anyway"

If your main job income is under £50,270 and your second job is also under that combined threshold, BR (20%) is correct. You're not losing money — you're just not getting the zero-rate band on the second job. The effective rate across both jobs may be lower than 20% when the PA is factored in across your full income.

"I left my main job and now the second job is my only job"

When your main employment ends, you should ask HMRC to update your tax code on the remaining job to 1257L (or whichever reflects your full PA). If you have a P45 from the old job, give it to the current employer — they can update the code. Otherwise contact HMRC directly.

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Summary: Second Job Tax at a Glance

You will not save tax by earning less — the marginal rate applies regardless of whether income comes from one job or two. What changes is the timing of how that tax is collected.