Few things generate more confused messages to payroll than a bonus payslip. You were promised £10,000, and what actually lands feels like a fraction of it, taxed at what looks like an outrageous rate. The good news is that in most cases, it isn't what it looks like, and the reason comes down to how PAYE handles a single large payment differently from a normal month's salary.
For your regular salary, use our take-home pay calculator. This guide covers what happens specifically when a bonus lands.
Why the Deduction Looks So Big
PAYE calculates tax cumulatively, based on your total income and allowance used so far in the tax year, recalculated every time you're paid. Most months this is invisible, since your pay is steady and the maths barely changes from one month to the next. A bonus breaks that pattern. It arrives as a single large spike in one specific month, and the cumulative calculation responds to that spike as though a much bigger chunk of your income needs taxing right now.
Here's what that looks like with real numbers. Someone earning £4,000 a month normally has £590.50 deducted in a typical month. If they receive a £10,000 bonus in December, taking that month's gross pay to £14,000, the tax deducted that month jumps to £4,250, an extra £3,659.50 compared to a normal month. On the bonus itself, that works out at an effective rate of 36.6% for that pay period, and it's easy to see why that feels like being taxed at nearly 40% for simply getting a bonus.
| Amount | |
|---|---|
| Tax in a normal month | £590.50 |
| Tax in the bonus month | £4,250.00 |
| Extra tax withheld that month | £3,659.50 |
Why It Usually Corrects Itself
This is the part that matters most, and it's genuinely good news. Cumulative PAYE isn't calculating your final tax bill in that one month, it's estimating based on what your total pay looks like if it continued at that rate. Once the bonus month passes and your pay returns to normal, the calculation adjusts, and by the end of the tax year, the total tax you've paid across all twelve months matches exactly what you'd owe if the same total annual income, salary plus bonus, had been paid evenly all year.
In the example above, someone earning £48,000 a year plus a £10,000 bonus has a correct total annual tax bill of £10,632. Run the cumulative calculation all the way through to the end of the tax year, and the total tax actually deducted comes to exactly £10,632 too. The bonus month feels painful in isolation, but it isn't an extra charge, it's your tax bill being front-loaded into that one payslip rather than spread evenly, and the months afterward correct the balance automatically.
The One Genuine Exception: Leaving Your Job
The self-correction relies on you staying in the same job for the rest of the tax year, so the cumulative calculation has later months to even things out. If you receive a large bonus and then leave shortly afterward, whether through resignation, redundancy, or retirement, there may not be enough remaining pay periods in that employment for the automatic correction to happen.
This doesn't mean the money is lost. If you start a new job before the tax year ends and hand over your P45, your new employer's cumulative calculation picks up where the old one left off and continues correcting things. If you don't start a new job before the tax year ends, HMRC typically reconciles the full year afterward and refunds any overpayment directly. Either way, you get it back, it just may take a little longer to arrive than if you'd stayed in the same job.
What About National Insurance?
National Insurance works differently from Income Tax in an important way: it's calculated separately for each pay period, not cumulatively across the year. There's no averaging or correction mechanism, each month simply stands on its own.
This actually works slightly in your favour with a lump-sum bonus. Because a big chunk of a bonus month's pay falls above the monthly Upper Earnings Limit, more of it gets taxed at the reduced 2% NI rate than would apply if the same total were spread evenly across twelve months. In the example above, concentrating the bonus into one month results in £124.85 less total National Insurance across the year than if the same £58,000 had been paid in equal monthly instalments. It's a similar effect to how splitting income across two separate jobs can reduce total NI, covered in our second job tax guide.
Ask your employer: If you're close to the £100,000 Personal Allowance taper zone and a bonus would push you over it, ask whether it can be paid partly or fully into your pension through salary sacrifice instead of as cash. This avoids the 60% effective marginal rate in that band entirely, rather than paying it and hoping for a later adjustment.
Common Mistakes
The most common one is assuming the bonus month's payslip reflects your true, permanent tax rate on that money. It almost never does, it reflects a snapshot of cumulative PAYE reacting to a spike, not your final annual position.
It's also easy to miss that a bonus can push you into territory covered elsewhere on this site, particularly the 60% tax trap if it takes your income over £100,000, where the maths genuinely does get worse and isn't just a timing illusion. Checking where a bonus lands you before it's paid, not after, is the only way to plan around it if that applies to you.