I think I've built a better annual leave calculator than GOV.UK. Here's my working.

I'm going to say something I probably shouldn't. I think my free annual leave calculator is better than the one on GOV.UK. Not more official. GOV.UK wins that before I open my mouth, and my own tool tells you in plain terms that it's guidance, not legal advice. But better at the actual job HR and payroll are doing all day? Yes. And since the whole thing is built to show its working, it seems only fair I show you mine.

Here's the case. Argue me down if you can.

Official and "best tool for the job" aren't the same thing

The GOV.UK holiday entitlement calculator does one thing, and does it fine. You answer the questions, it hands you a number: full leave year, starters and leavers, accrual for irregular-hours and part-year staff. For a five-days-a-week, nothing-unusual employee, that's all you need.

But anyone who's ever run HR or payroll knows annual leave questions have a nasty habit of turning up disguised as simple sums and turning into something else entirely. Is this person really an irregular-hours worker, or just labelled one? Days or hours? Are the bank holidays inside the allowance or on top? Are we working out entitlement, or holiday pay, which are not the same thing? And the one that ruins a Friday afternoon: six months later, when someone challenges the figure, can anyone actually remember how it was worked out?

That last question is the one I built for.

Mine doesn't just give you the number. It gives you the decision.

Annual Leave Logic shows its working. It produces the entitlement, then records the method and the assumptions sitting behind it, flags anything that looks like it needs a second pair of eyes, and drafts the wording you'd actually send a manager or payroll.

A normal calculator answers "what are they entitled to?" Mine answers "what are they entitled to, why, what did you assume, is anything here risky, and how will you explain it when someone asks?" That's the real job. I'm genuinely surprised more tools don't work this way.

The market's already good. That's what makes this fun.

I didn't invent holiday maths, and I'm not going to pretend I did. There are strong free tools out there. Breathe handles days, hours and the common pro-rata cases. Timetastic does full-year and pro-rata. Moorepay has a properly useful 12.07% accrual calculator for irregular-hours and part-year workers.

So I'm not competing on the calculation. Everyone can spit out a number. I'm competing on everything that happens before and after it.

Then the law changed, and most employers missed it

Here's where a "nice to have" feature grew teeth.

From 6th April 2026, employers have a legal duty to keep records of annual leave and holiday pay, including carry-over and what each payment included, and to hold those records for six years. Failing to keep adequate records can amount to a criminal offence and expose an employer to a fine.

And it arrived quietly. The duty wasn't in the government's own implementation roadmap. Employment lawyers found it buried in the commencement regulations when they were published, days before it took effect. Which means a lot of employers still have no idea it exists.

This isn't groundwork for some distant policy idea either. The Fair Work Agency launched on 7th April 2026, and statutory holiday pay enforcement is due to move into its remit from 2027. The government is consulting right now on how that regime will work, and the proposals are not gentle: powers to investigate underpayments going back up to six years, penalties of up to 200% of arrears capped at £20,000 per worker, and the ability to review an employer's whole workforce rather than a single complaint. The consultation closes on 22nd September 2026. Your six-year records are exactly what you'd be producing.

So picture the challenge landing three years from now. Which record would you rather be holding?

"Balance: 73.5 hours."

Or: "Balance: 73.5 hours. Here's the working pattern, the contractual entitlement, the leave-year dates, how we treated bank holidays, and the exact calculation that produced it."

Quite.

The honest bit, because I'm not going to insult you. My calculator does not make you compliant on its own. The new duty is about your ongoing records: leave taken, carry-over, the pay components, tracked over years. What my tool gives you is the defensible note of how a given entitlement was reached. It sits alongside your record-keeping and makes it stronger. It doesn't replace it.

Anyone selling you "compliance in a box" is selling you something.

Part-time, zero-hours, and the labels that lie

This is where the cheap calculators get dangerous. Statutory leave is 5.6 weeks, which comes to 28 days at most, and only if you work five or more days a week. For truly irregular-hours and part-year workers, the 12.07% accrual method applies to leave years starting on or after 1 April 2024.

But problems don't arrive with the right legislation stapled to them. Someone gets called "casual" or "term time" or "bank" or "variable hours", and that label tells you almost nothing about the calculation that should follow. My tool nags you to describe the actual arrangement instead of trusting the label, and it keeps entitlement, accrual and pay in separate boxes, because blurring the three is how expensive mistakes happen. That's not clever arithmetic. It's HR judgement built into the thing.

So. Better than GOV.UK?

For legal authority? No. Don't be daft. GOV.UK is the source of truth and I'll be first to say so.

For an employer, HR lead or payroll team who needs to see how the answer was reached, what was assumed, what to send payroll, what to double-check and what to keep on file? Then yes. I think mine's the better tool. Not because it knows employment law GOV.UK doesn't. Because it's built around the way these decisions really happen inside real organisations, awkward labels, tight deadlines and all.

The government calculator gives you an answer.

Mine gives you the file note you'll want when someone asks why.

And that's a much harder thing to build.

Last reviewed: August 2026. This article is general guidance, not legal advice.