📅Dates
Date tools handle calendar calculations: difference between dates, business days, exact age, holidays, time zones and countdowns. Useful for deadlines, planning and any situation where counting days by hand invites mistakes.
72 tools
Mayan Haab Calendar Converter
Convert a Gregorian date to the Mayan Haab civil calendar (365 days), with 18 months of 20 days plus the Wayeb. Discover your day in the Mayan calendar.
Perpetual Calendar (1583+)
View the full calendar of any year (1583 onward) with Brazilian national holidays marked and ISO week numbering.
Doomsday Rule (Conway)
Mentally calculate the day of week for any date using Conway's Doomsday Rule, with step-by-step anchor and doomsday of year.
Swatch Internet Time
Convert current time or any time to Swatch .beat (1 beat = 86.4s), format @000 to @999 with no time zone.
Local Sidereal Time (GMST/LST)
Calculates Greenwich Mean Sidereal Time (GMST) and Local Sidereal Time (LST) for geographic coordinates and a specific date, used in amateur astronomy.
Rata Die Converter
Convert dates between the Gregorian calendar and Rata Die (Reingold/Dershowitz), the serial number used in bibliography and history systems.
Fiscal Week and Broadcast Calendar
Convert dates between fiscal week (4-4-5, 4-5-4, 5-4-4) and Broadcast Calendar (NABBA, week starts on Monday), with adjustable fiscal year.
Zeller Congruence — Day of Week
Compute the day of week for any date using Zeller Congruence — 1882 algorithm requiring only modular arithmetic. Shows each step (q, m, K, J, h) for didactic purposes. Supports Julian and Gregorian calendars.
International Fixed Calendar Converter (Cotsworth)
Convert a Gregorian date to the International Fixed Calendar (Cotsworth, 1902) — 13 months of 28 days + a 'Year Day' outside any month + a 'Leap Day' on leap years. Used internally by Kodak from 1928 to 1989. Shows month name (with 'Sol' between June and July) and weekday.
French Decimal Time Converter
Convert a normal time (HH:MM:SS) into French revolutionary decimal time, where the day has 10 hours of 100 minutes of 100 seconds each, and back. A curiosity from the 1793 French Revolution.
Brazilian Long Weekend Planner
Maps every Brazilian holiday of the year and shows which days to take off so that a couple of vacation days turn into long weekends.
One Date in 12 Calendars
Enter a date and see how it is written in the Hebrew, Islamic, Persian, Indian (Saka), Coptic, Ethiopic, Buddhist, Chinese, Japanese and other calendars.