Coverage and methods
Data sources
Each published result should be traceable to a named rule set. This page records the coverage, source version, and browser dependency behind all four calculators.
U.S. federal holiday calculations
The calculator counts Monday through Friday, then deducts observed U.S. federal holidays defined by the bundled rule set. Rule version: 2026-08-11. Last reviewed: 2026-08-11.
- U.S. Office of Personnel Management federal holiday calendars
- OPM “in lieu of” holiday rules
- 5 U.S.C. § 6103 — Holidays
- 5 U.S.C. § 6104 — Holidays for daily, hourly, and piece-work employees
Included: the eleven recurring federal holidays in 5 U.S.C. § 6103(a), with the standard Saturday-to-Friday and Sunday-to-Monday observation rules used for a Monday–Friday week. Excluded: Inauguration Day, state and local holidays, one-time executive closures, company holidays, and alternative work schedules.
Stored OPM fixtures cover 2021, 2022, 2026, and 2027. Other supported years are projected from published holiday and observation rules.
Users should compare a projected result with the applicable OPM calendar and their organization’s policy once published.
How calendar-day calculations work
- Enumerate every civil date in the selected Gregorian calendar year.
- Count Monday through Friday as weekdays.
- When holiday exclusion is on, deduct observed federal holidays that land on those weekdays.
- Keep the annual and monthly totals derived from the same date list.
Business Days uses the same holiday bundle when that option is enabled, but also applies the selected weekend and shutdown dates. Overlapping exclusions are deducted once. Add and subtract modes begin with the next or previous civil date, so the starting date is not day one.
Both calculations run in the browser and do not depend on a live OPM request.
Week rules and time zones
The Week Number calculator bundles the reviewed Unicode CLDR snapshot46-bundled-v1 (reviewed 2026-08-19) for regional first-day and minimum-days defaults. ISO mode follows ISO 8601-1:2019.
- ISO 8601-1:2019 for ISO week-date rules.
- Unicode CLDR date data for regional week conventions.
- IANA Time Zone Database for named-zone transitions.
- ECMAScript Internationalization API, implemented by browser
Intl, for local formatting and time-zone calculations.
The Time Zone Meeting Planner uses the visitor’s browser Intl implementation for offsets and transitions. Its bundled city index, reviewed 2026-08-19, helps discovery but does not supply offset rules. Browsers can briefly lag a new government time-zone change, so results may differ until vendors update their bundled IANA data.
Report a data issue
Email info@gteamtool.com with the tool name, selected year or rule, expected result, and a public source that supports the correction.