Date & Time Calculators

Date and time calculators handle the surprisingly tricky arithmetic of the Gregorian calendar: leap years (every 4 years except century years not divisible by 400 — so 1900 was not a leap year but 2000 was), variable month lengths, and jumping across the Gregorian calendar reform of 1582 (or 1752 in British territories). Every calculator uses the JavaScript Date object which correctly handles the full Gregorian calendar with millisecond precision.

Common calculations covered: age from birth date, time between two dates in years/months/days/hours/minutes, working days between two dates (excluding weekends and configurable holidays), date offset (add or subtract N days/weeks/months/years from a starting date), day of week for any historical or future date, and countdown timers to specific target dates.

Time zones are handled via IANA time zone identifiers (America/New_York, Europe/London, Asia/Tokyo, etc.) with automatic Daylight Saving Time transitions. Time zone conversion calculators show the current time in multiple zones simultaneously, useful for coordinating meetings across regions or verifying international deadline compliance.

Business-day calculators support US federal holidays by default (New Year's Day, MLK Day, Presidents Day, Memorial Day, Juneteenth, Independence Day, Labor Day, Columbus Day / Indigenous Peoples Day, Veterans Day, Thanksgiving, Christmas), with optional customization for state/provincial holidays or company-specific closure dates. Some calculators support UK bank holidays, Canadian statutory holidays, or configurable holiday sets.

These tools are used by HR (accrued PTO, service milestones, retirement date planning), legal professionals (statute of limitations, filing deadlines, contract terms), project managers (Gantt chart date arithmetic, milestone tracking), and general users (birthday countdowns, anniversary calculators, "days until vacation").

Reviewed by the ScoutMyTool editorial team. Formulas verified against primary authoritative sources.