If you run a business in the UK, you would reasonably expect employment law to work something like this:
- Parliament creates the law.
- GOV.UK explains the law.
- Employers follow the instructions.
- HR and payroll software apply the rules.
Simple.
Unfortunately, anyone who has spent enough time dealing with HR, payroll or workforce management knows that it is rarely quite that straightforward.
At Chronicle, we regularly have to take UK employment legislation and Government guidance and turn it into UK employment law software real, working code that has to produce the right answer for every employee, every time. And that has taught us something:
Reading an employment rule is one thing. Turning it into an exact calculation that works for thousands of employees is something entirely different.
Software Can’t Answer “It Depends”
Take annual leave.
The headline rule sounds extremely simple:
Most workers are legally entitled to 5.6 weeks of paid holiday each year.
But then you start building a system to calculate it.
What happens when someone:
- Starts halfway through the holiday year?
- Leaves halfway through the holiday year?
- Works three days rather than five?
- Works different hours each day?
- Changes their working pattern during the year?
- Works irregular hours?
- Is employed for only part of the year?
- Goes on maternity, paternity or other statutory leave?
- Is absent because of sickness?
- Has contractual holiday above the statutory minimum?
- Has the holiday carried forward?
- Changes from full-time to part-time employment?
- Has an entitlement containing fractions of hours or days?
Suddenly, “5.6 weeks” is no longer a particularly simple software requirement.
An HR professional can review an unusual situation and make a judgement based on the facts. A computer cannot. Eventually, Chronicle has to return a number:
- 17.5 days.
- 124.25 hours.
- 3.62 hours accrued this month.
There is no button in the source code labelled “It’s complicated.”
The Difficult Part Is Converting Words Into Rules
Government guidance is primarily written for people. Software is written using logic. Those are not always particularly compatible things.
A piece of guidance might use perfectly reasonable phrases such as:
- normally
- relevant period
- reasonable opportunity
- regular payments
- average earnings
- where appropriate
- part of a leave year
A person can read those phrases within their wider context. Software ultimately needs something much more precise:
IF this is true, THEN do this.
ELSE, do something else.
That distinction becomes critical when you are developing HR, payroll, or Time & Attendance software. A difference that looks insignificant when reading a paragraph of guidance can materially change someone’s holiday entitlement once it becomes a calculation.
Holiday Entitlement Is a Good Example
The rules surrounding holiday entitlement have become increasingly sophisticated. For example, specific statutory rules now apply to irregular-hours and part-year workers.
For applicable leave years, holiday entitlement for these workers accrues at 12.07% of the hours worked during a pay period. There are then specific rules governing rounding, plus further rules covering holiday accrued while an irregular-hours or part-year worker is on sick leave or statutory leave.
Holiday pay itself introduces another set of considerations, including normal remuneration, regular overtime, commission and reference periods. Rolled-up holiday pay can be used for certain irregular-hours and part-year workers, but not simply applied universally across a workforce.
None of those individual rules is necessarily unreasonable. The difficulty comes when all of them have to coexist within one system, which is exactly the challenge behind any holiday requests and entitlement tool worth using.
Then Come the Edge Cases
This is where software development becomes particularly interesting. You can build functionality that handles 95% of employees perfectly. Then somebody asks:
“What happens if…?”
What follows is usually a working arrangement sufficiently unusual that nobody involved in originally designing the feature had considered it. And yet it may be completely legitimate.
At that point, we go back through:
- GOV.UK guidance
- The underlying legislation
- ACAS guidance
- Worked Government examples
- Previous legal decisions where relevant
- Professional or legal advice where necessary
We then have to decide exactly how the software should behave. Sometimes intelligent, experienced people can read the same piece of guidance and initially interpret it differently. That isn’t necessarily because either interpretation is ridiculous. It’s often because legislation has been written to establish a legal principle, not to provide a software specification.
The Government’s Calculator Says X — But Why?
Government calculators can be extremely useful. We use them ourselves when testing Chronicle. But from a software development perspective, knowing the Government calculator produces an answer isn’t always enough. We also need to know why it produced that answer.
Consider an employee joining midway through a holiday year. There may be several ways somebody could reasonably imagine calculating their pro-rata entitlement. Should it be calculated using:
- Exact calendar days?
- Complete months?
- A monthly accrual method?
- Working days remaining?
- Contracted hours?
- A particular statutory formula?
The answer depends upon the circumstances and the relevant rules. For a software provider, simply reproducing an answer isn’t sufficient. We need to understand the calculation behind it, because the next employee might have completely different circumstances.
This Isn’t Just an HR Software Problem
Employers face the same difficulty. HR teams are expected to understand legislation covering areas including:
- Holiday entitlement
- Holiday pay
- Statutory leave
- Sickness
- Working time
- National Minimum Wage
- Flexible working
- Family-related leave
- Employment status
- Record keeping
Large organisations may have dedicated HR, payroll and legal teams. A company employing 30 people may have one person responsible for the lot. That person opens GOV.UK expecting to find a simple answer. Sometimes they do. Sometimes they find themselves opening six browser tabs and wondering whether they understood the first page correctly. See our FAQ for the questions we’re asked most often.
The Rules Also Change
There is another complication for providers of UK employment law software: employment legislation doesn’t stand still.
Holiday entitlement rules affecting irregular-hours and part-year workers changed significantly from April 2024. From 6 April 2026, employers are also required to retain detailed records relating to annual leave and holiday pay for at least six years.
When rules change, software providers cannot simply alter a formula and press Publish. We also have to consider:
- Existing employees
- Existing holiday years
- Historic calculations
- Previous working patterns
- Payroll integrations
- Customer configuration
- Reporting
- Audit trails
- Employees changing between different working arrangements
A calculation made two years ago still needs to be explainable two years later. That makes good record-keeping and auditability just as important as getting today’s calculation right, something we build into every module of our workforce management software, from scheduling through to payroll. It’s why several of our customers, including Bridgnorth Aluminium, rely on Chronicle to keep complex, multi-site holiday records consistent.
There Is a Better Way
One improvement we would like to see is significantly more implementation-focused Government guidance. Alongside complicated employment legislation, Government departments could publish comprehensive official test scenarios — not just two or three basic examples, but a proper dataset. For example:
Scenario 1
- Employee start date: 17 September
- Holiday year: 1 January – 31 December
- Working pattern: 5 days per week
- Annual entitlement: 28 days
- Expected statutory result: X
Scenario 2
- Employee start date: 17 September
- Working pattern: Monday, Tuesday and Thursday
- Hours vary by day
- Annual entitlement: statutory minimum
- Expected statutory result: X
Scenario 3
- Irregular-hours worker
- Hours worked this pay period: 73.5
- Relevant leave year: X
- Expected accrued entitlement: X
Then include the difficult scenarios: employees changing hours, employees leaving, sickness, statutory leave, part-year working, rounding, and changing contractual entitlements.
If the Government produced an official suite of perhaps 100 or 200 test cases alongside significant calculation-based employment legislation, software companies could run automated tests against them. Payroll providers could do the same. Employers could check difficult cases. HR professionals could understand how a particular interpretation had been reached. And employees would have greater confidence that their entitlement was being calculated correctly.
That’s How Software Development Already Works
This is essentially how modern software is tested. A developer creates a rule. We create known inputs. We define the expected output. Then we test the software automatically:
Input A + Rule B = Expected Result C.
If the result changes unexpectedly, the test fails. Applying the same methodology to Government guidance would remove a surprising amount of ambiguity. Instead of every HR software company independently interpreting the same paragraph, everyone could test against the same authoritative scenarios.
Complexity Has a Real Cost
This matters because legislative complexity has a cost. If a rule takes hours for an experienced HR professional, payroll specialist or software developer to interpret, that cost ultimately falls somewhere.
It falls on employers. It falls on software providers. And eventually, it can fall on employees when rules are unintentionally applied incorrectly.
Clearer implementation guidance isn’t about weakening employment rights. Quite the opposite. The easier a statutory right is to understand and implement correctly, the more consistently that right is likely to be applied.
Building HR Software Gives You an Unusual Perspective on Employment Law
At Chronicle, our job is to take complicated workforce rules and make them simple for the person actually using the system. Ideally, an HR manager shouldn’t need to understand every formula running behind the scenes. They should be able to enter the correct information and trust the system to produce the correct result.
But somebody has to understand those rules. And when you’re the company writing UK employment law software, you very quickly discover the gap between:
“The law says…”
and:
“So what exactly should the software do?”
Those two things aren’t always as close together as you might expect.
Want to see how this works in practice? Get in touch with the Chronicle team.
This article discusses UK employment legislation and guidance from a software implementation perspective and is not intended to constitute legal advice. Employers should obtain appropriate professional advice where they are uncertain about their legal obligations.
