Second Job Tax in the UK: Rates, Codes and How to Avoid a Bill

Your first payslip from a second job often looks like a mistake. A fifth of it has gone in tax from the very first pound, while your main job seems to tax you far less. Nothing is wrong yet, but this is also how people end up with a surprise letter from HMRC a year later.

Second job tax follows a few simple rules once you see them laid out. This guide covers the rate your extra pay is really taxed at, the codes each job should have, how National Insurance and student loans are handled, and what to check so the total comes out right.

How second job tax works

There is no separate tax on a second job. You get one Personal Allowance of £12,570 and one set of tax bands for all your employment income added together. HMRC usually gives the whole allowance to the job that pays most, and the second job is taxed at whichever rate your combined income reaches, often 20% from the first pound.

Each employer only sees its own payroll, so the tax code on each job is HMRC’s way of telling that employer how much to take. If the codes match your real total, the tax is right. If they do not, the difference is settled after the tax year ends on 5 April.

How much tax do you pay on a second job?

The rate depends almost entirely on what your main job pays, because that decides where in the tax bands your second income starts. The table shows the Income Tax rate on second job pay for England, Wales and Northern Ireland in 2026/27.

National Insurance comes on top only if the second job itself pays more than £12,570 a year. A second job paying £10,000 alongside a £30,000 salary is therefore taxed at 20% and nothing else, while the same job alongside a £55,000 salary is taxed at 40%.

When second job tax reaches 60%

If your combined income passes £100,000, you lose £1 of Personal Allowance for every £2 above that line, until it is gone at £125,140. Extra pay in this range is taxed at 40% and also takes away allowance, which works out at an effective 60%. A second job is often what pushes people into this band without them noticing, since neither employer sees the total.

Second job tax codes

The code on your second job tells that employer which rate to use. These are the codes you are most likely to see.

HMRC sets the code from what it expects you to earn across the year. If your pay changes, the code may stop matching, so it is worth checking both codes whenever your hours or salary move. The tax code checker breaks down any code you are unsure of.

Which box to tick on the starter checklist

A new job without a P45 asks you to fill in a starter checklist. If you are keeping another job or receive a workplace or State Pension, choose Statement C. That tells payroll to use BR straight away. Ticking A or B by mistake gives the second job 1257L as well, so you get the allowance twice and payroll takes too little. If you are put on 0T or an emergency code while HMRC catches up, our guide to the emergency tax code explains how that unwinds.

Splitting your Personal Allowance between jobs

When your main job pays less than £12,570, part of your allowance sits unused while the second job is taxed at 20% on everything. HMRC can move the unused part across. With £8,000 from one job and £7,000 from another, £4,570 of allowance can go to the second job, so only £2,430 of it is taxed, at a cost of £486 instead of £1,400.

You can ask for this through your Personal Tax Account, the HMRC app or by phone. A split works best when both jobs pay steady amounts, because a change in hours can leave one job with too much allowance and the other with too little.

National Insurance on a second job

National Insurance is worked out separately in each job. You only pay employee NI in a job once your pay there passes £242 a week or £1,048 a month, and each job has its own threshold. So two jobs paying £12,000 each attract no employee NI at all, even though a single £24,000 salary would.

The rule can work against higher earners. Each job charges 8% up to its own £50,270 limit, so two well-paid jobs can take more NI than one salary of the same total. HMRC refunds anything above the yearly maximum after the tax year, and you can apply to defer contributions in one job if you expect to go over it.

Student loan repayments with two jobs

Payroll checks each job against your plan’s threshold on its own. On Plan 2, with a threshold of £29,385, a £15,000 second job takes nothing even if your main salary is well above the threshold. That changes if you file a Self Assessment return, because repayments are then worked out on total income and the shortfall is added to your tax bill. The second job tax calculator shows both figures if you add your plan.

Do you need to tell HMRC about a second job?

For a normal employed second job, no form is needed. Your new employer reports your pay to HMRC each time you are paid, and HMRC updates your codes from that. You should still check your Personal Tax Account or the HMRC app a few weeks after starting, because the income estimate HMRC holds for each job drives the codes.

Contact HMRC yourself if any of these apply.

• Your combined pay will go over £50,270, or £43,662 in Scotland, so part of the second job needs a higher rate code.
• Your main job pays less than £12,570 and you want the allowance split.
• One of the jobs has ended, so the other can take back the full allowance.
• Your second income is self-employed and above £1,000 a year.

When your second job is self-employed

Side income from freelancing, deliveries or selling services is taxed through Self Assessment rather than payroll. The first £1,000 of trading income a year is covered by the trading allowance, so very small amounts need no return. Above that, you register for Self Assessment by 5 October after the tax year ends and pay by 31 January.

Your salary usually uses the Personal Allowance, so self-employed profit is taxed at 20% or more from the first pound above the trading allowance or your expenses. Class 4 National Insurance is added at 6% on profits between £12,570 and £50,270 and 2% above, and unlike Income Tax it looks at self-employed profit on its own, not your salary.

Making Tax Digital now applies to people whose self-employed and property income is over £50,000, falling to £30,000 from April 2027 and £20,000 from April 2028. Your salary does not count towards those limits.

Second job tax in Scotland

Scottish taxpayers use the same codes with an S in front, such as SBR, and a wider set of D codes because Scotland has more bands. Many Scottish workers on a typical salary are already in the 21% intermediate band, so a second job on SBR at 20% can leave a small shortfall, and SD0 is the code that matches. The table shows the rate on second job pay in Scotland.

What happens if you pay too much or too little

After 5 April, HMRC compares the tax your employers took with the tax due on your total income. If the figures differ, you receive a P800 or Simple Assessment letter between June and March of the following year. Smaller underpayments are usually collected through your tax code over the next year, while amounts over £3,000 are billed through Simple Assessment with a payment deadline. Overpayments are refunded to your bank account or by cheque.

The cheapest way to sort out second job tax is catching a wrong code during the year, when HMRC can spread the correction over your remaining payslips. Running both jobs through the second job tax calculator shows whether your current codes collect the right total.

Is a second job worth it after tax?

Looked at per £100 earned, a basic rate taxpayer with a second job under £12,570 keeps £80, since only 20% Income Tax applies. If that job pays more than £12,570, NI takes it down to £72 on the part above the threshold. For someone whose main salary is already over £50,270, the figure drops to £60 or less, and inside the £100,000 to £125,140 band it can fall to £40 before NI. Student loans take a further £9 where the second job passes the plan threshold.