# payroll.tax-period
Every PAYE and National Insurance calculation starts by asking which tax week
or tax month a payment falls in. The answer depends only on the date the
employee is paid, never on the dates the work was done: a monthly salary paid
on 28 April is month 1, and one paid on 3 May is still month 1.
- Tax week 1 is 6 to 12 April, week 2 is 13 to 19 April, and so on. Week 52
ends on 3 or 4 April, so the last one or two days of every tax year (5 April,
or 4 and 5 April when the tax year contains 29 February) are **week 53**.
- Tax month 1 is 6 April to 5 May, month 2 is 6 May to 5 June, and so on to
month 12, 6 March to 5 April.
- `period` is what `payroll.income-tax` and the other payroll capabilities
take. For monthly pay it is the tax month. For weekly, fortnightly and
four-weekly pay it is the tax week of the pay date, because HMRC's
cumulative tables for those frequencies are indexed by week: a fortnightly
payroll paid in weeks 2, 4, 6 uses the week 2, 4 and 6 figures. A payday in
week 53 is the extra payday of the year and HMRC calls it week 53 (weekly),
week 54 (fortnightly) or week 56 (four-weekly); those periods are taxed on a
non-cumulative basis, which is why they get their own numbers.
This capability does not check that a payroll really is fortnightly or
four-weekly (that the paydays are 14 or 28 days apart); it places one date.
Sources: HMRC, "Employer further guide to PAYE and NICs" (CWG2), sections on
tax weeks and months and on week 53 payments,
https://www.gov.uk/government/publications/cwg2-further-guide-to-paye-and-national-insurance-contributions;
HMRC, "Specification for PAYE tax table routines" v24.0, paragraph 14 (payments
in weeks 53, 54 or 56),
https://www.gov.uk/government/publications/payroll-technical-specifications-income-tax.
## Before you rely on this
**Not professional advice.** This capability calculates payroll figures from published rules. It is a software component for developers, not tax or legal advice. Rules change and every rate here has an effective date. Check that the dates cover your case. Verify results against the official sources listed above, and have a payroll specialist review how you use it, before anyone relies on the output. Provided "as is" under its licence, without warranty.
**Unreviewed.** This capability's implementations agree in every language and pass its published test vectors, which were worked out from the official sources cited. But no qualified payroll specialist has yet checked those vectors, or confirmed that the capability covers the cases it claims. Treat it as a draft. Do not use it for real people, money or decisions without your own expert review. Once a qualified reviewer signs off, this notice is replaced with their name, qualification and the date. Each new version needs fresh sign-off.
## Notices
Contains public sector information licensed under the Open Government
Licence v3.0 (https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/).
1.0.1 marks it unreviewed and adds its attribution notices (NOTICE). The code and the tests are unchanged.