Why is My Bonus Taxed So Much? What Really Happens to a One-Off Payment

The complaint is universal and the explanation is almost never the one people expect. No country on this site charges a distinct, higher rate of tax on bonus income. What several of them do is withhold it using a method designed for evenly spread monthly salary, which produces a number that looks wrong in the month it lands and then quietly corrects itself later.

Three separate things get confused in this conversation: the rate you actually owe, the rate withheld at the time, and the marginal rate the bonus pushes you into. They are rarely the same.

What you actually owe

A bonus is ordinary employment income. It is added to your salary, and the combined figure is taxed under the normal brackets. That means the bonus is taxed entirely at your marginal rate, which is higher than your effective rate by definition, because it sits on top of everything else.

Take a British employee on £50,000 who receives a £5,000 bonus. Annual income becomes £55,000. Net pay rises from £39,520 to £42,457. The bonus was worth £2,937 after tax, so £2,063 of it went in deductions, an apparent rate of 41.3%.

Nothing unusual happened. The £50,270 higher rate threshold sat £270 above the salary, so almost the entire bonus was taxed at 40% with National Insurance at 2% on top. The same bonus paid to someone on £40,000 would have kept £3,600 of itself, because it would have stayed inside the basic rate band. The difference is where the salary sits, not what kind of payment it was. The mechanics of that threshold are covered in what a £50,000 UK salary actually leaves.

What gets withheld, which is a different question

The gap between owing and withholding is where most of the frustration lives, and each system creates it differently.

Flat supplemental withholding: the United States

American employers may treat a bonus as supplemental wages and withhold federal income tax at a flat 22%, rising to 37% on amounts above $1 million in a year. Add Social Security and Medicare at 7.65% and roughly 29.65% disappears at source.

For someone in the 22% bracket that is almost exactly right. A $5,000 bonus on an $80,000 salary carries a true cost of 29.6%, so the flat method lands within a few dollars. For someone in the 32% or 35% bracket the flat 22% actually under-withholds, and the shortfall shows up as a bill in April. The method feels harsh and is frequently generous.

Cumulative PAYE: the UK and Ireland

British and Irish payroll is cumulative, meaning each pay run recalculates tax for the year to date rather than treating the month in isolation. That is usually accurate, but in the month a large bonus is paid the system sees a spike in cumulative income and taxes it at the rate that spike implies.

If the bonus genuinely pushes you into a higher band for the year, the deduction is correct and permanent. If it does not, subsequent months automatically refund the excess through reduced deductions. Nothing needs to be claimed. The exception is a bonus paid in month twelve, where there is no remaining payroll to correct it and the refund waits for the annual reconciliation.

Annualisation: Germany and Austria

German payroll treats a bonus as a sonstiger Bezug, an irregular payment. The tax is worked out by calculating the annual tax on your salary alone, then on your salary plus the bonus, and deducting the difference. It is mathematically the correct answer, but it produces a large single deduction that has no relationship to any previous payslip.

One quirk works in your favour. Social contributions have annual ceilings: health and long-term care stop at 66,150 euros, pension and unemployment at 90,600. A bonus that takes you past a ceiling carries no further contributions on the excess, which is why German bonuses at higher salaries retain more than employees expect.

The Austrian exception

Austria is the outlier worth knowing about. The thirteenth and fourteenth salary payments, the Urlaubsgeld and Weihnachtsgeld, are taxed at a flat 6% rather than at the marginal rate, within limits. That is not a withholding quirk, it is a genuine and unusually generous rule, set out in the guide to Austria's 13th and 14th salaries.

The bonus that costs more than it pays

In a handful of situations a bonus can trigger a loss larger than the payment itself, because it crosses a threshold that withdraws something.

• The UK personal allowance taper. Between £100,000 and £125,140 the allowance withdraws at £1 for every £2, producing an effective 60% band. A bonus landing in that range keeps 40 pence in the pound, as set out in the £100,000 tax trap.
• Child benefit charges. A UK household loses child benefit progressively between £60,000 and £80,000. For three children the effective marginal rate over that stretch can exceed 65%.
• Means tested childcare and housing support. Withdrawn on income across most of Europe, and the taper rates are rarely published anywhere convenient.
• Tax credit phase-outs. The Dutch labour credit and the Finnish earned income credit both shrink as income rises, adding several points to the real rate on any additional payment.

What actually reduces the bill

Three things work, and none of them involves asking payroll to use a different code.

1. Divert it into a pension before it is paid. A bonus sacrificed into a pension avoids income tax and, in most systems, social contributions on both sides. At a 42% or 56% marginal rate this is the single most efficient use of a one-off payment, and it is the core argument in the guide to salary sacrifice.
2. Time it across a tax year boundary. Splitting a large bonus across two years can keep both halves below a threshold. This is only available where the employer is willing, but it is worth asking.
3. Check the reconciliation. Where withholding was provisional, as in the United States or in any month twelve payment, the correction arrives through the annual return rather than automatically.