A second income, whether that is Saturday shifts, a weekday evening job or something you sell online, brings a set of tax questions that catch people out in predictable ways. The most common one is being handed a BR tax code and assuming HMRC has made a mistake. Usually it has not. Occasionally it has, and knowing the difference is worth a few hundred pounds.
You get one Personal Allowance, not one per job
Everything follows from this. The £12,570 Personal Allowance is yours once, across all your income, not once for each employer. Your main job normally uses the whole of it and carries the standard 1257L code. Your second job then has nothing left to set against it, so HMRC issues a code that taxes every pound from that job.
| Code on the second job | What happens | When HMRC uses it |
|---|---|---|
| BR | All income from that job taxed at 20% | Your other income keeps you within the basic rate band |
| D0 | All income from that job taxed at 40% | Your other income already uses up the basic rate band |
| D1 | All income from that job taxed at 45% | Your other income already exceeds £125,140 |
| 0T | No allowance, but taxed through the bands | Often a placeholder when HMRC lacks details |
Add an S in front for Scottish rates or a C for Welsh, so SBR and CBR mean the same thing under the relevant rates for those nations.
A worked example where BR is exactly right
Main job £30,000 on 1257L. Second job £8,000 on BR.
The second job pays 20% on all of it, so £1,600 of tax, leaving £6,400. Combined income is £38,000, entirely within the basic rate band, so 20% is precisely what should have been charged. Nothing more is owed and nothing is due back. BR did its job.
And one where it is not
Main job £46,000 on 1257L. Second job £8,000 on BR.
Combined income is £54,000. The higher rate threshold is £50,270, so £3,730 of that income belongs in the 40% band. BR only collected 20% on the second job, which leaves a shortfall of 20% of £3,730, or £746.
HMRC will find it, usually after the tax year ends, and will normally collect it by adjusting a later tax code rather than sending a bill. That is fine, but it means a year of quietly under-taxed pay followed by a year of visibly over-taxed pay. If you know a second job will push you over £50,270, ring HMRC on 0300 200 3300 and ask them to code it correctly from the start.
Splitting your allowance between two jobs
If neither job on its own uses your full allowance, BR overcharges you during the year. Take two jobs at £12,000 each. Left alone, the first job uses the whole 1257L allowance and pays £0 tax on £12,000 while the second job pays 20% on all £12,000, which is £2,400. The correct annual figure on £24,000 of total income is 20% of £11,430, which is £2,286. You have overpaid £114 and will wait until after April to see it.
HMRC can split the allowance across both jobs instead, giving you something like 628L on one and 629L on the other, so the tax comes out right as you go. You have to ask. It is a phone call, not a form, and it is worth making if your two jobs are of similar size.
National Insurance works completely differently
National Insurance is charged per employment, per pay period, and the two jobs are not added together. Each employer applies the primary threshold of £1,048 a month independently.
So two jobs at £12,000 each, £1,000 a month from each, produce no employee National Insurance at all. Someone earning the same £24,000 from a single employer pays 8% on everything above £12,570, which is £914.40 a year. That is a genuine and entirely legal difference, and it is one of the few places where the system quietly favours the person with two jobs.
There is a catch worth knowing. A qualifying year for the State Pension needs earnings at or above the lower earnings limit, £559 a month in 2026/27, in a single employment. Earnings from separate jobs are not added together for that test. Two jobs of £400 a month each therefore give you neither National Insurance to pay nor a qualifying year. Our article on what National Insurance buys you goes through the qualifying year rules properly.
If you are on a high salary in both jobs you can end up overpaying National Insurance across the two. HMRC can grant a deferment, which shows on your payslip as category letter J or Z, and any overpayment can be reclaimed after the year end.
Side income that is not a job
Selling, freelancing, letting a room, driving: none of this goes through PAYE, so the rules are different again.
The trading allowance gives you up to £1,000 of gross trading income each tax year with no tax to pay and, in most cases, nothing to tell HMRC about. There is a separate £1,000 property allowance for income from land or property. Note that both apply to gross income, not profit, so £1,100 of sales with £900 of costs still takes you over the line.
Go above £1,000 of gross trading income and you must register for Self Assessment. The deadline is 5 October following the end of the tax year in which you crossed it, so income earned in the year to 5 April 2026 needed registering by 5 October 2026. Miss it and penalties start accruing.
The main filing dates then follow: 31 October for a paper return, 31 January for an online one, and 31 January for paying what you owe, with payments on account potentially due on 31 January and 31 July. If you want a modest amount collected through your tax code instead of paying a lump sum, file online by 30 December rather than the end of January, and check the conditions on GOV.UK because not every situation qualifies.
One useful distinction: selling your own second-hand belongings is not trading and is not taxable. Buying things in order to sell them at a profit is. Online platforms now report seller data to HMRC, so the question of which side of that line you are on is more likely to be asked than it once was.
Practical Checks
Look at your tax codes across both jobs together rather than one at a time. Between them they should account for exactly one Personal Allowance. If you see 1257L on both, something is wrong and you are heading for an underpayment, which is worth fixing before it becomes a bill. Our emergency tax code article covers what to do when a code is plainly incorrect, and you can model the combined position with the net pay calculator by entering each job separately and adding the results.
This page is general information about how second incomes are taxed, not tax advice, and the figures are for the 2026/27 tax year. HMRC's Personal Tax Account shows all your live tax codes in one place, which is the quickest way to see whether the two jobs are being taxed sensibly, and a call to 0300 200 3300 fixes most coding problems in one go.