How the calculators work, and what they leave out

Each calculator on this site turns a section of the law into arithmetic. This page says which section, which date decides which figure, how the result is rounded and what the calculator leaves out. All the statutory values live in one parameter file, dated 5 October 2026, and every page reads them from there.

Redundancy pay

Service is counted in complete years back from the relevant date, at most 20 (Employment Rights Act 1996, section 162). A year of employment earns one and a half weeks’ pay if you were 41 or over for the whole of it, one week if you were 22 or over, half a week otherwise; the calculator takes your age on the first day of each year of service, so a year that begins on your 41st birthday counts at one and a half. The official ready reckoner uses your age on the relevant date and counts each earlier year as one year younger; the two methods agree except when a birthday falls on the first day of a year of service, and the year-by-year table shows which applies to you.

The relevant date is the day notice expires or, without notice, the day the dismissal takes effect (section 145). When the employer gives less than the statutory notice, section 145(5) moves the date to the end of that notice for the two-year test, the count of years and the ages. The weekly cap, £751 in Great Britain and £783 in Northern Ireland, is the one in force on the relevant date before that extension, as the transitional article of the Increase of Limits Order 2026 provides. Caps back to April 2022 are in the file, so earlier dismissals are priced correctly.

Checked against: the test cases of the GOV.UK redundancy calculator (its code is published as alphagov/smart-answers), the worked examples on nidirect, and the maximum payments of £22,530 and £23,490.

Notice

Section 86: nothing before one month of service, one week up to two years, then one week per complete year up to twelve; one week from an employee. A shorter contractual term is overridden. Service is measured on the day notice is given, and notice runs from the following day.

Holiday entitlement and holiday pay

Days: 5.6 times the days worked per week, never more than 28. Hours: 5.6 weeks of the average day, with days capped at five, the method of the GOV.UK holiday calculator. A starter receives the share of the leave year left, counted in months, rounded up to the next half day; a leaver receives the exact share of days, and the payment in lieu follows regulation 14: (A × B) − C.

Irregular-hours and part-year workers in Great Britain accrue 12.07 % of the hours worked in each pay period, a fraction of an hour rounded to the nearest hour, for leave years starting on or after 1 April 2024 (regulation 15B); rolled-up holiday pay is the same percentage of pay (regulation 16A). Those amendments extend to Great Britain only (SI 2023/1426, regulation 1), so the Northern Ireland option keeps 5.6 weeks.

A week’s holiday pay for variable pay is the average of the last 52 weeks in which pay was received (regulation 16). Regular overtime, commission and seniority pay are included for the first four weeks; the last 1.6 weeks may be paid at basic rate for regular-hours workers, and at the full normal rate for irregular-hours workers.

Maternity, paternity, adoption and shared parental pay

Weeks run Sunday to Saturday. The qualifying week is the 15th week before the expected week of childbirth; employment must have started 25 weeks before the Saturday that ends it, and average weekly earnings must reach the lower earnings limit in force on that Saturday (£129 for 2026/27). SMP and SAP pay six weeks at 90% of average weekly earnings, truncated at seven decimals and rounded up to the penny each week, then the lower of the flat rate (£194.32) and 90%. The flat rate changes with the first pay week that starts on or after the first Sunday of April, the rule used in HMRC’s calculator; weeks after April 2027 are priced at the 2026/27 rate and marked, because the next rate has not been published. Source: HMRC rates and thresholds 2026 to 2027.

Paternity leave in Great Britain has no qualifying period since 6 April 2026 (Employment Rights Act 2025, section 16); Northern Ireland keeps 26 weeks and a 56-day window (nidirect). Shared parental leave is 52 weeks less the maternity or adoption leave taken, and shared parental pay 39 weeks less the weeks of SMP, SAP or Maternity Allowance used, as in the GOV.UK example.

Statutory Sick Pay

For sickness starting on or after 6 April 2026: no waiting days, no lower earnings limit, a weekly rate equal to the lower of £123.25 and 80% of normal weekly earnings (SI 2026/373). The daily rate is the weekly rate divided by the number of qualifying days, cut at four decimals; each pay week is rounded up to the penny. These are HMRC’s published daily-rate tables, which the tests reproduce line by line. The calculator does not price a spell that began before 6 April 2026, where transitional rules apply.

What the calculators do not do

• No income tax or National Insurance: all amounts are gross.
• No contractual or collective-agreement terms unless you enter them (extra redundancy pay, contractual notice, extra holiday).
• No decision on fairness, discrimination or employment status: they assume you are an employee, or a worker where the right covers workers.
• Breaks in continuous employment, TUPE transfers and weeks that do not count are not modelled: enter the start date your employer uses for continuous service.

Tests and updates

Automated tests run before every release: official reference cases for redundancy, holiday, maternity and sick pay, bounds (service just under two years, ages 21, 22, 40 and 41, the 20-year limit, the caps, the 28-week sick pay limit) and every page’s figures, which come from the same functions. Rates are reviewed every April and whenever a commencement order or up-rating order is made. A reported error is checked against the source, fixed, and turned into a test.