The formula behind time-and-a-half pay, worked out step by step.
If you've ever looked at a payslip and wondered how the extra hours were worked out, you were looking at overtime pay. In the UK, there's no single legal formula for this the way there is in some countries — overtime pay is set by your employment contract, not by statute. This guide explains what the law actually requires, what most employers do in practice, and how to work out an overtime figure once you know the rate your contract uses.
Employers in the UK do not have to pay extra for overtime at all. There's no statutory overtime rate, and no legal requirement for time-and-a-half or double time — those are contractual arrangements, not legal minimums. What your contract says is what applies: some contracts pay overtime at the normal hourly rate, some pay an enhanced rate (such as 1.5x or 2x), and some offer time off in lieu (TOIL) instead of extra pay.
There is one legal floor, though: your average pay for all hours worked must not fall below the National Minimum Wage (or the National Living Wage, for workers aged 21 and over). If unpaid overtime would drag your average hourly pay under that rate, your employer is breaking the law, regardless of what the contract says.
Separately, the Working Time Regulations 1998 cap the average working week at 48 hours, unless you've agreed in writing to opt out. That's a limit on hours, not a pay rule, but it's worth knowing alongside the pay rules above.
Many employers do choose to pay an enhanced overtime rate, and 1.5x ("time and a half") is a common choice, even though it isn't required by law. If your contract specifies a threshold and a multiplier, the maths behind it is three steps:
Say someone's contract pays £20 an hour, with overtime at 1.5x after 40 hours in a week, and they work 45 hours.
Now say someone on £32 an hour, same 40-hour threshold and 1.5x rate, works 48 hours.
You can check either example instantly with the Overtime Calculator — enter the same numbers and confirm the totals match. The calculator's threshold and multiplier are both adjustable, so you can match them to whatever your own contract actually says.
Not every contract pays a premium for overtime — many simply pay the normal hourly rate for every hour worked, with no enhanced multiplier at all. Someone on £25 an hour who works 44 hours, with no overtime premium in their contract, is simply paid for all 44 hours at £25.
To model this on the Overtime Calculator, set the multiplier to 1.0 rather than 1.5 — the calculator will then show every hour paid at the same rate, matching a contract with no overtime premium.
If you work part-time, your employer will normally pay your standard hourly rate for any hours worked beyond your contracted hours, up to what a full-time colleague would work. Overtime rates (if your employer offers them) typically only kick in once you pass full-time hours, or if you're working unsocial hours that a full-time colleague would also be paid extra for — your contract will say which applies to you.
There is no statutory overtime rate in the UK — how overtime is paid depends on your employment contract, and your average pay must not fall below the National Minimum Wage. For the full rules, see GOV.UK's overtime: your rights page. Estimates only. Not legal, tax, or payroll advice.