How to work out pro-rata holiday for a new starter

Grace starts on 1 August. Your leave year runs from January to December and everyone gets 21 days. She has missed seven months of the year, so she shouldn't get all 21, and she has five months still to work, so she shouldn't get none. The question is what goes in between, and the answer is a short sum with one judgement call at the end.

Method one: by days left in the leave year

Count the calendar days from the person's first day to the last day of the leave year, both days included, and divide by the number of days in the year. Multiply the allowance by that share.

For Grace, 1 August to 31 December is 153 days, and 2026 has 365:

153 ÷ 365 × 21 = 8.80 days

This is the most exact method, because it gives someone who starts on 1 August slightly more than someone who starts on 20 August, which is fair. It is also the method ToDoing uses.

Method two: by whole months

Divide the allowance by twelve to get a monthly rate, and multiply by the number of months left. For Grace that is 21 ÷ 12 = 1.75 days a month, for five months:

5 × 1.75 = 8.75 days

The two methods give almost the same answer when someone starts on the first of a month. They drift apart when someone starts mid-month, because the monthly method has to decide whether a part month counts. Take Daniel, who starts on 15 September. By days, 15 September to 31 December is 108 days:

108 ÷ 365 × 21 = 6.21 days

By months, he gets 3.5 months if you count his half of September (6.13 days), 3 months if you only count whole months from October (5.25 days), or 4 if you count September in full (7 days). That spread is the reason to pick one method and write it down, rather than deciding case by case.

Rounding

Nobody books 6.21 days of leave, so the result has to be rounded, and the direction matters. Rounding up to the nearest half day is the common choice and the safest one. In the UK, at the time of writing, part days of statutory holiday can be rounded up but never down. Other countries have their own rules, so check before you settle on rounding down.

Rounded up to the half day, Grace gets 9 days and Daniel gets 6.5. ToDoing rounds the same way, so the figure on someone's balance card matches the figure you would work out by hand.

Leave years that don't start in January

The method is the same for any leave year: count from the start date to the last day of that leave year. If your year runs from April to March and Grace still starts on 1 August, she has 243 days of the year left, from 1 August to 31 March:

243 ÷ 365 × 21 = 13.98, which rounds up to 14 days

If the leave year includes 29 February, divide by 366 instead.

Part-timers

Someone who works fewer days a week gets a share of the full-time allowance in proportion to the days they work. A person working three days a week, where full time is five, gets three fifths:

3 ÷ 5 × 21 = 12.6 days a year

If they also start mid-year, apply both shares. Joining on 1 August, three days a week:

12.6 × 153 ÷ 365 = 5.28, which rounds up to 5.5 days

Leavers

The same sum works in reverse for someone who leaves part-way through the year: count from the start of the leave year to their last day. Subtract what they have already taken, and the difference is what they are owed, or what they have taken beyond their share. What happens to that last figure, whether it is paid out or deducted, depends on their contract and on local law, so it is worth agreeing before it comes up.

The calculator

The free pro-rata leave calculator does the days method for any allowance, any start and end date and any leave year, and rounds up to the half day. If you also need to know how many working days a stretch of dates contains, with weekends and public holidays left out, the working days calculator does that for Kenya, South Africa, England and Wales, and the US.

In ToDoing, joiners are handled for you. Set a person's start date, and any leave type set to pro-rate gives them their share automatically, on the balance card they see when they book. A part-timer's allowance, or anything else agreed with one person, is set on them directly, with a note saying why, and it overrides the policy for that year. For leavers, the calculator is still the quickest way to the figure.