- Day of the Week Calculator
- A tool determining the day of the week (Mon–Sun) for any past, present, or future calendar date. Day of the Week →
- What Day Was I Born
- A search query determining the exact day of the week associated with an individual's birth date. Day of the Week →
- ISO Week Number
- An international standard (ISO 8601) numbering weeks 1 through 52/53, beginning on Monday. Day of the Week →
- Day of the Year (1–366)
- The ordinal day number representing chronological progress through a calendar year (e.g., Feb 1 = Day 32). Day of the Week →
- Zeller's Congruence
- An algorithm created by Christian Zeller to calculate the day of the week for any Gregorian calendar date. Day of the Week →
- Leap Year Rule
- Years divisible by 4 are leap years, except century years unless also divisible by 400. Day of the Week →
- Perpetual Calendar
- A calendar valid for many years designed to look up the day of the week for any given date. Day of the Week →
- Solar Calendar
- A calendar system whose dates indicate the position of Earth in its revolution around the Sun.
- Lunar Calendar
- A calendar based upon monthly cycles of the Moon's phases (e.g., Islamic or Hebrew calendars).
- Equinox
- The time of year when day and night are of approximately equal length (Vernal in March, Autumnal in Sept).
- Solstice
- The calendar days when the Sun reaches its highest or lowest point (Summer Solstice / Winter Solstice).
- First Day of the Week
- Sunday in US/Canada standard conventions; Monday according to international ISO standards. Day of the Week →
- Weekend Days
- Non-working days traditionally including Saturday and Sunday in Western business standard practices. Working Days →
- Fortnight
- A unit of time equal to 14 consecutive days (2 full calendar weeks). Date ± Days →
- Quarter (Q1, Q2, Q3, Q4)
- A 3-month financial period: Q1 (Jan–Mar), Q2 (Apr–Jun), Q3 (Jul–Sep), Q4 (Oct–Dec).
- Bimonthly
- An event occurring either once every two months or twice in a single month.
- Biweekly
- An event occurring every two weeks (26 times per year).
- Semi-Annual
- An event occurring twice per year, spaced six months apart.
- Centennial
- A 100th anniversary or a time period extending across a full century.
- Millennium
- A period of time equal to 1,000 calendar years.