Sources & Evidence Standards
The legislation, government guidance and regulator material behind our leave and pay calculators — plus the rules we use to decide which source controls a calculation.
LeaveCalculators.com uses official primary and first-party sources. We start with legislation and regulations, then use government departments, employment regulators and statutory bodies to confirm how those rules are applied in practice. We do not copy formulas from competing calculators, forum posts, generic HR blogs or AI-generated summaries. When a rule differs by state, province, territory, worker type or effective date, that distinction is handled explicitly rather than being flattened into one universal answer.
Why the source behind a leave calculator matters
A leave calculator can look precise while still being wrong. A result such as “16.8 days”, “4% vacation pay” or “12 weeks” may be mathematically tidy, but the calculation is only useful if the rule behind it applies to the person using the tool. Employment rights depend on jurisdiction, employment status, length of service, work pattern, leave year, earnings, employer coverage and sometimes the exact date on which the entitlement arises.
That is why we treat sourcing as part of the calculator itself, not as a footnote added after the code is written. Before a formula is implemented, we identify the legal framework, the official guidance that explains it, the eligibility conditions, any caps or reference periods, and the circumstances in which a different rule must be used.
For example, the United Kingdom’s statutory annual leave framework is not the same as Ireland’s, Australia’s or New Zealand’s. Canada has 13 provincial and territorial employment-standards systems plus a separate federal jurisdiction. In the United States, federal law does not create a general right to paid vacation, while the Family and Medical Leave Act provides qualifying employees with job-protected unpaid leave and individual states may provide additional paid-leave or sick-leave rights. Treating all of those systems as if they worked alike would make a calculator simpler to build, but much less reliable.
Our source hierarchy
Not every source has the same legal weight. We therefore use a simple hierarchy when researching and reviewing calculators. The purpose is to separate the rule itself from explanatory material and from sources that are useful only as background.
Legislation and regulations
Acts, regulations, statutory instruments and official legislation databases are used to establish the legal basis of an entitlement. Where legislation and a simplified explanatory page appear to conflict, we investigate the underlying law rather than silently choosing the easier wording.
Government guidance
Official government pages often explain eligibility, calculation methods and worked examples more clearly than legislation does. These pages are especially useful for translating a legal rule into calculator inputs and user-facing explanations.
Regulators and statutory bodies
Employment regulators and statutory bodies help confirm how rules are administered in real workplaces. Examples include Acas in Great Britain, the Fair Work Ombudsman in Australia and the Workplace Relations Commission in Ireland.
State, provincial and territorial sources
Where the national position is incomplete or does not control the entitlement, we use the relevant local authority. This is essential for Canada and the United States, and also for matters such as Australian long service leave.
What we do not use as the legal basis of a calculator
Third-party HR articles, payroll-company summaries, law-firm marketing pages, Reddit discussions, search snippets and other calculators can sometimes help us spot an issue worth checking. They are not treated as the authority for a statutory formula. If a third-party page says one thing and the official source says another, the calculator follows the official framework unless a later legal development requires further investigation.
Official sources by country
The links below are the core official sources used across LeaveCalculators.com. Individual calculator pages may cite additional regulations, benefit pages, state agencies, provincial authorities or technical guidance where the calculation requires them. This list is therefore a foundation, not an exhaustive legal bibliography.
United Kingdom
For UK holiday entitlement and pay, we use GOV.UK guidance alongside the Employment Rights Act 1996, Working Time Regulations 1998 and relevant Acas material. GOV.UK confirms that almost all workers are entitled to 5.6 weeks of statutory paid holiday, with a 28-day statutory cap for someone working six days a week or more.
Holiday-pay calculations can also depend on work pattern and pay type, so the source used for entitlement is not automatically sufficient for holiday pay.
Australia
For national workplace entitlements, our starting point is the Fair Work Act 2009 and the Fair Work Ombudsman’s guidance on the National Employment Standards. The Fair Work Ombudsman states that employees other than casual employees receive paid annual leave under the NES, while awards and registered agreements can provide more generous terms but not less than the NES minimum.
Long service leave is different: the applicable rule may come from a state or territory law or, in some circumstances, a pre-modern award or agreement. Calculators covering it must therefore identify the relevant jurisdiction before applying a formula.
Canada
Canada requires especially careful jurisdiction handling. There are 10 provinces and 3 territories with their own employment-standards rules, plus a separate federal labour-standards regime for federally regulated workplaces. A province-level rule should not be presented as the law for every Canadian worker.
For federally regulated employees, Canada.ca explains annual vacation entitlements under the Canada Labour Code, including vacation time and vacation-pay percentages that increase with service. Provincial and territorial calculators use the relevant government or employment-standards source for that jurisdiction.
United States
The United States cannot be treated as a single paid-leave system. The U.S. Department of Labor states that the Fair Labor Standards Act does not generally require payment for time not worked, such as vacation, sick leave or holidays. State and local laws may create additional rights, so calculators must be tied to the correct jurisdiction.
At federal level, the Family and Medical Leave Act provides eligible employees of covered employers with up to 12 workweeks of job-protected leave for qualifying family and medical reasons, subject to detailed eligibility and employer-coverage conditions.
New Zealand
Employment New Zealand and the Holidays Act 2003 are the current basis for leave calculations. Under the present framework, employees become entitled to at least four weeks of annual holidays after 12 months of continuous employment, and the way a “week” is represented depends on the employee’s working arrangement.
A major change is already legislated but not yet in force: the Employment Leave Act 2026 will replace the Holidays Act on 6 August 2028. Until that commencement date, our calculators continue to apply the current Holidays Act rules rather than switching early to the future system.
Ireland
Irish leave calculators use legislation from the Irish Statute Book together with Workplace Relations Commission guidance and the relevant Department of Social Protection material where a state benefit is involved. The WRC states that most employees are entitled to four working weeks of paid annual leave, with statutory calculation methods based on hours or time worked and a maximum of four normal working weeks.
We keep statutory annual leave separate from other rights such as statutory sick leave and social-welfare benefits because different Acts, eligibility tests and payment mechanisms may apply.
How we handle new laws, future rules and effective dates
Employment law often changes in stages. A government may announce a policy, Parliament may pass legislation months later, regulations may supply the detail after that, and the operative provisions may not commence until a future date. A calculator should not treat all four stages as if the new rule already applies.
We therefore record both the publication or enactment date and the effective date that matters to the calculation. If a law has passed but is not yet in force, we may explain the upcoming change while continuing to calculate under the law that currently applies.
The same principle applies to annual statutory-rate changes. A rate announced for a future tax year or benefit year is not substituted into a current-period calculation before its official start date. Where a calculator lets users choose a historical or future period, the applicable rate table must correspond to that selected period.
What happens when official guidance changes before legislation does?
Guidance can be revised to explain a court decision, regulatory change or administrative practice. When that happens, we check whether the change affects the mathematical formula, eligibility, definitions, examples or simply the wording. Material changes trigger a calculator review. Editorial-only changes do not automatically mean the underlying formula has changed.
How a source becomes calculator logic
Linking to an official page is not enough. The difficult part is converting a written employment rule into logic without dropping the conditions that make the rule correct. Our methodology separates the source into several pieces before implementation:
- Scope: which country, state, province or territory controls the result?
- Eligibility: does the rule depend on worker status, employer size, service length, hours worked, earnings or another qualifying condition?
- Formula: what is multiplied, divided, averaged or capped?
- Reference period: which pay weeks, service period, leave year or earnings window must be used?
- Rounding: does the official guidance specify a rounding method, or should the tool preserve precision until the display stage?
- Exceptions: are there special rules for irregular hours, casual workers, shift workers, part-year work, federally regulated employment or local legislation?
- Effective date: which version of the rule applies to the user’s selected date?
This is also why two calculators may legitimately use different-looking formulas even when both concern “annual leave”. Similar labels do not mean the legal mechanisms are interchangeable.
When official sources are unclear or incomplete
Government guidance is written for broad audiences and cannot anticipate every employment pattern. Legislation can also contain definitions, cross-references and exceptions that do not convert neatly into a short online form. Where a result would depend on facts we do not collect, we do not manufacture certainty.
Instead, the relevant calculator should do one or more of the following: request the missing input, limit the calculation to the scenario it can handle, show the assumption being made, explain that a different rule may apply, or direct the user back to the relevant official authority. This is particularly important for contractual entitlements that exceed the statutory minimum, collective agreements, unusual payroll arrangements and disputes about employment status.
August 2026 source audit notes
Our source list is reviewed alongside the calculators it supports. The entries below record material points confirmed during the latest source-page review rather than pretending that every government page changes on the same schedule.
Who reviews these sources?
Ruby Miller
HR & Employment Law Content Lead
Ruby researches the statutory frameworks behind LeaveCalculators.com, checks official-source changes against calculator logic and maintains the editorial notes that explain eligibility, assumptions and limitations. The aim is not to replace professional advice, but to make the rule behind each estimate visible enough for a user to understand and verify.
Source questions we are often asked
Does LeaveCalculators.com use government sources?
Yes. Government legislation databases, official departments, employment regulators and statutory bodies are the core sources used to build and review our statutory leave and pay calculators. The relevant source should also be identifiable from the calculator page itself.
Do you use other calculator websites to set your formulas?
No. Other tools may help reveal a question worth investigating, but their output is not treated as the authority for our calculation. We trace the rule back to legislation, regulations or first-party official guidance.
Why can leave rules differ inside the same country?
Because employment law is not always administered at one national level. Canada has provincial, territorial and federal labour jurisdictions, the United States has federal, state and sometimes local requirements, and Australia has state or territory rules for some entitlements such as long service leave.
What if a new law has passed but has not started yet?
We keep calculating under the rule currently in force and identify the future change separately. A passed Act is not automatically the rule for today if its operative provisions have a later commencement date.
How often are sources checked?
Checks are tied to the update pattern of the rule rather than one arbitrary sitewide schedule. Known annual rate changes, newly enacted legislation, government guidance revisions and material corrections can all trigger a review. Each calculator should show the date its underlying figures were last verified.
Are official sources always easy to interpret?
No. Some rules depend on definitions, exceptions or facts a short calculator cannot capture. Where the official framework does not support one universal result, we disclose assumptions and limitations instead of presenting an estimate as definitive.
Can I report an outdated or incorrect source?
Yes. If an official link has moved, a rate has changed or you believe our interpretation no longer reflects the current rule, please use the Contact page. Material corrections are handled under our Editorial Policy.
Want to check how a formula is built?
Read the calculation methodology, or flag a source that you believe needs another review.