Day of the Week Calculator - Kostenloser Online-Rechner

Day-of-the-week calculator answers the trivia-friendly question 'what day was it?' or 'what day will it be?' for any historical or future date. India's Independence Day, 15 August 1947, was a Friday. Mahatma Gandhi's birthday 2 October 1869 was a Saturday. The next solar eclipse on 14 October 2027 will be a Thursday. Beyond trivia, this calculator helps with practical questions: 'what day is my next birthday in 2027?' (useful for planning leave or parties), 'what weekday will the next financial year start on?' (1 April), 'when does Diwali 2027 fall on a working day?'.

The calculator works for any date from year 1 to 9999 using JavaScript's Date API, which uses the proleptic Gregorian calendar (the modern calendar projected backwards even for periods when other calendars were in use). For Indian context: the British East India Company switched India to the Gregorian calendar with the Calendar (New Style) Act in 1752; before that, Indian regions used various luni-solar calendars (Vikram Samvat, Saka, regional almanacs). The Hindu calendar still influences festival dates today, calculated via panchang astronomy. This calculator also shows day-of-year, ISO week number, and leap-year status - useful for academic and business contexts.

Day of week calculation: the JavaScript Date object returns 0 for Sunday, 1 for Monday, ..., 6 for Saturday. Internally, this is computed using Zeller's congruence or similar formula that tracks accumulated days from a reference epoch. The proleptic Gregorian calendar is used - every year is governed by Gregorian leap-year rules, even pre-1582 (when most of Europe switched from Julian).

Leap year rule: a year is a leap year if divisible by 4, EXCEPT centurial years (divisible by 100) are not leap years UNLESS also divisible by 400. So 2000 was a leap year (divisible by 400). 1900 was not (div by 100, not by 400). 2100 will not be. This 400-year cycle keeps the calendar synchronised with the solar year (average year length is 365.2425 days vs Earth's actual 365.24219).

Day-of-year: 1 to 365 (or 366 in leap years). 1 January is day 1; 31 December is day 365/366. Useful for academic calendar tracking (which day of the academic year is today?), financial year tracking (1 April is day 1 of Indian FY), and astronomy/agriculture (planting and harvest cycles tied to day-of-year). ISO week number: weeks count from 1 to 52 or 53, where week 1 is the week containing the first Thursday of the year. Differs slightly from common 'first Monday of January' convention.