Second Job Tax UK: How Much Will You Actually Keep?

Most people take on a second job expecting to pocket nearly everything they earn. Then the first payslip arrives and roughly 20% to 40% has vanished before they've spent a penny. Here is what the tax rules for a second job in the UK actually mean for your take-home pay, and how to stop HMRC taking more than it is legally owed.

Why Your Second Job Gets Taxed So Hard

The UK personal allowance sits at £12,570 for the 2025/26 tax year. That is the amount you can earn entirely free of income tax. The catch: you only get one personal allowance, and HMRC assumes your main employer is already using all of it.

So when a second employer runs your payroll, HMRC instructs them to apply a tax code with no personal allowance attached. The most common one is BR, which stands for Basic Rate. Every pound you earn from that second job is taxed at 20% from the first penny. No free slice at the bottom, no adjustment for how much you actually earn overall.

If your combined income from both jobs tips you above £50,270, the portion of second-job income above that threshold is taxed at 40%. HMRC uses a D0 code in that scenario, meaning 40% is deducted on everything from that employer, even if not every pound actually sits above the higher-rate threshold.

The blunt instrument nature of BR and D0 codes is the source of most second-job tax overpayments. HMRC's system was not designed to be precise in real time; it was designed to ensure the government does not undercollect. That asymmetry costs workers money.

The Real Numbers: How Much Tax on a Second Job?

Let's be specific. Say you work as a warehouse operative earning £28,000 from your main job and you take on weekend shifts at a supermarket earning an additional £6,000 a year.

Your main job uses your 1257L tax code, meaning the first £12,570 of your £28,000 is tax-free. You pay 20% on the remaining £15,430, which is £3,086 in income tax.

Your second job is assigned a BR code. The supermarket deducts 20% on your full £6,000, collecting £1,200 in tax. But here is the thing: your total income is £34,000, which is comfortably below the £50,270 basic-rate limit. You are paying the right rate (20%), but you are still paying on every pound of that £6,000. That is the design, not a mistake.

Now consider a different scenario. You earn £46,000 from your primary employer and pick up £8,000 from a second job as a delivery driver. Your total income is £54,000.

The first £4,270 of second-job income (taking you to the £50,270 threshold) is taxed at 20%. The remaining £3,730 is taxed at 40%. But if HMRC has assigned you a D0 code on the second job, your employer deducts 40% on the full £8,000, collecting £3,200. The correct liability is closer to £2,346. That is an overpayment of £854 sitting with HMRC, which you will eventually get back but only if you claim it.

Checking whether your codes are correct is the single fastest financial fix most employees can make. Use the free tool at /check-my-tax-code to see what HMRC currently holds on record for you.

When a BR Code Is Actually Correct

Before you fire off a complaint to HMRC, it is worth understanding when BR is the right code.

If your main job income already uses up your full personal allowance and your second job income sits entirely within the basic-rate band (meaning total income is below £50,270), then BR is technically correct. You are paying 20% on your second-job earnings, which is the right rate. You are not getting a second personal allowance, but you are not entitled to one either.

The problem arises in two specific situations:

Situation one: Your main job income is low enough that you have unused personal allowance. If you earn only £8,000 from your main job, for instance, you have £4,570 of personal allowance sitting unused. HMRC can reallocate some of that allowance to your second employer via a split code, but it will not do so automatically. You have to ask. The post How to Split Personal Allowance Between Jobs covers exactly how to request that adjustment.

Situation two: You have a D0 code but your second job income does not all fall above the higher-rate threshold. This is the overpayment scenario described above, and it is surprisingly common among workers with two jobs where total income hovers around £50,000 to £55,000.

The Emergency Tax Problem on New Second Jobs

There is a third scenario that catches people off guard: starting a second job mid-year without a P45 or a completed starter checklist.

If your second employer cannot verify your situation, HMRC may instruct them to apply an emergency tax code. Depending on which statement you ticked on the starter checklist (or whether you ticked any), you could end up on 1257L week 1/month 1, which treats every pay period as if it is the first of the year, or on BR, or in some cases on 0T, which is even more aggressive and removes your entire personal allowance with no basic-rate relief either.

The fix is not complicated but it requires action on your part. Completing your starter checklist accurately tells your new employer which statement applies to your situation, and that information flows directly to HMRC via Real Time Information payroll submissions. If you have already started and the wrong code is in place, contacting HMRC's Income Tax helpline on 0300 200 3300 or updating your details via your Personal Tax Account will prompt a corrected coding notice.

For a broader look at how tax codes behave when you start any new role, Tax Code New Job UK: What Actually Happens on Day One is worth reading alongside this.

Do You Need to File a Self Assessment Return?

Having a second job does not automatically trigger a Self Assessment obligation, but it can.

HMRC requires you to file a Self Assessment tax return if your total income from employment (across all jobs) exceeds £100,000, if you have untaxed income above £1,000 from other sources, or if HMRC cannot collect the correct tax through PAYE alone. For most people with two standard employed jobs, PAYE handles everything and no return is needed.

However, if you are doing ad hoc work paid without PAYE, such as cash-in-hand shifts, freelance invoices, or gig economy payments, that income may need to be declared separately. The £1,000 trading allowance means you can earn up to that amount from casual work without reporting it, but anything above requires registration.

If you do end up in Self Assessment territory, the Tax Refund Estimate Before Self Assessment: Do the Maths Now post will help you understand whether you are likely to owe more or receive a refund before you file.

What to Do If You Have Been Overpaying

If you suspect you have paid too much tax on a second job, here is the process.

First, check your tax codes across all employments. Your payslip shows the code your current employer is using. Your Personal Tax Account at gov.uk shows what HMRC holds on record. If they do not match, that discrepancy alone is worth investigating. You can also use the free checker at /check-my-tax-code to flag inconsistencies quickly.

Second, calculate the potential overpayment. If you have been on D0 but not all your second-job income was higher-rate, work out the difference between what was deducted and what should have been deducted at 20%.

Third, contact HMRC. You can call the Income Tax helpline or submit a query through your Personal Tax Account. HMRC can issue a repayment directly to your bank account, typically within a few weeks of the claim being processed. For context on how long that process actually takes, HMRC Repayment Faster via Personal Tax Account: Does It Work? is a useful read.

For overpayments in previous tax years, you can claim back up to four years. A claim for 2021/22 overpayments, for instance, must be submitted before 5 April 2026.

The National Insurance Angle

Income tax is not the only deduction to understand. National Insurance Contributions (NICs) are calculated separately by each employer, with no crossover between jobs.

This means if you earn £20,000 from your main job and £15,000 from a second job, each employer applies the NIC thresholds independently. The primary threshold for 2025/26 is £12,570 per year (£1,047.50 per month). You pay 8% Class 1 NICs on earnings between that threshold and £50,270 from each employment separately.

In practice, this means you could end up paying NICs on the same band of income twice, once at each employer, whereas a single employer paying you £35,000 would only apply NICs once across that total. HMRC does operate a deferment scheme for people who overpay NICs across multiple employments, but you generally need to apply for it; it does not happen automatically.

If your combined employment income is in the higher-income bracket, the interaction between NICs, the personal savings allowance, and any benefit-in-kind from your main employer can also affect your effective tax rate in ways that are not obvious from a payslip alone. Private Medical Insurance Tax Code: What Your Employer Didn't Tell You covers one of the more common examples of benefit-in-kind affecting your coding.

The One Action Worth Taking Today

The question in the title, how much tax on a second job in the UK, has a simple answer in principle: 20% or 40% depending on your total income. But the real question is whether HMRC is collecting the right amount through the right mechanism, and the honest answer is that for a significant minority of workers with multiple jobs, it is not.

BR codes applied where unused personal allowance exists, D0 codes applied to income that partially falls in the basic-rate band, emergency codes never corrected after a new start, and NIC deferment claims never made: each of these is a quiet, ongoing overpayment that HMRC has no incentive to flag to you.

You started reading this because you wanted to know what a second job would actually cost you in tax. The answer depends entirely on whether your codes are set correctly. Find out in under five minutes at /check-my-tax-code. If something is wrong, the correction is straightforward. If everything is correct, you will at least know exactly what you are dealing with.