The formula
How to calculate annual hours
Annual hours matter for pro-rata calculations, hourly rate comparisons and annualised-hours contracts. The contracted figure and the figure actually worked differ by five or six weeks of leave.
Fifty-two weeks is the standard multiplier, though a calendar year is 52.18 weeks. Payroll systems generally use 52, which is why annual salary divided by 52 gives the weekly figure on a payslip.
Fill in the following:
- Contracted hours per week (hours)
- Annual leave (days)
- Bank holidays (days)
- Days worked per week (days)
No submit button: type and the answer moves. Your inputs end up in the link, so the page can be shared already filled in.
Some of the fields above will accept figures that seem unusual for your own situation, and that is deliberate: the formula behind annual hours works the same way regardless of scale, so the calculator does not stop you testing a hypothetical scenario a long way from your actual numbers — often the fastest way to see which input the result is most sensitive to.
Why annual hours matters
The formula behind annual hours is standard and has not changed in decades; what changes is the situation it gets applied to. Two households can run the identical calculation and land on very different conclusions once their own numbers — income, rate, term, balance — are dropped in, which is why a generic textbook example is less useful than a calculator you can adjust to match your own circumstances.
It is also useful as a sense check before signing anything. A quote, an offer letter or a spreadsheet from someone else can contain an error, an optimistic assumption, or simply a different convention for rounding — running the same inputs through an independent calculator is a quick way to confirm a number before relying on it.
The reason a page like this exists at all, rather than leaving the calculation to a spreadsheet or a textbook appendix, is that the formula behind annual hours is fiddly enough to get wrong by hand but not complicated enough to need specialist software. That middle ground — real enough maths to matter, simple enough to check instantly — is exactly what a dedicated calculator is for, and it is why the same figure recalculated here should match a careful manual calculation almost exactly.
Where the same calculation needs to be run for several different scenarios side by side — three loan offers, two savings plans — the fastest approach is usually to open the calculator in a second browser tab for each one, so that the results can be compared directly rather than overwriting each other in a single set of fields.
Worked example
A concrete run-through, using the values already in the fields:
- Contracted hours per week: 37.5 hours
- Annual leave: 25 days
- Bank holidays: 8 days
- Days worked per week: 5 days
That gives:
- Contracted annual hours: 1,950 hours
- Hours actually worked: 1,702.5 hours
- Hours per working day: 7.5 hours
These figures are only the calculator's own starting values, included so the working is visible rather than hidden inside the tool above. Replace them with your own numbers and the same arithmetic applies — nothing about the method changes, only the inputs feeding it.
Reading the result
The difference between contracted and worked hours is what paid leave costs an employer. On these figures it is around 250 hours, or 13% of the contracted total.
Where this goes wrong. Unpaid breaks are not working time. A 9-to-5 with an hour for lunch is 35 hours a week, not 40, and using the wrong figure throws off every hourly rate derived from it.
A useful check on any unfamiliar result is to compare it against a rough mental estimate first — round the inputs to convenient numbers and see whether the calculator's answer lands in roughly the same territory. A wildly different figure usually means one of the fields was entered in the wrong unit, most often a percentage typed as a whole number where a decimal was expected, or the reverse.
A full-time UK job at 37.5 hours a week is 1,950 contracted hours, or roughly 1,700 after 25 days of leave and 8 bank holidays. At 40 hours a week it is 2,080 contracted.
One where the total is agreed for the year rather than the week, so hours can vary seasonally while pay stays level. Common in education, agriculture and some manufacturing.
The answer it gives you is contracted annual hours. With 37.5 hours contracted hours per week, 25 days annual leave and 8 days bank holidays, that comes to 1,950 hours. Change any field and the figure moves with it.
Whenever one of the underlying figures changes — a new interest rate, a different balance, an updated term — since the result only reflects what is currently in the fields. There is no need to keep a separate record of past results; the web address for a filled-in version already carries the figures used to produce it.
Not unless a tax rate or a fee is explicitly one of the inputs above. Where it is not, the figure shown is a gross calculation, and any tax due depends on your personal circumstances and current tax rules, which are worth checking separately.
The arithmetic itself is exact — the calculator applies the formula shown above precisely, with no rounding until the final figure is displayed. The uncertainty, where it exists, is entirely in the inputs: an estimated rate or an approximate balance carries that same approximation through to the result.