--- title: "What Day of the Week Was It? Old Date Finder | Past Crumbs" description: "Find the weekday of any date from 1 to 9999 CE, read as it was written at the time: Julian or Gregorian, with Britain's 1752 gap and Old Style years." url: https://pastcrumbs.me/ --- # What day of the week was it? Enter a date from a letter, a parish register or a diary. We read it the way it was written at the time, then show the weekday, the same day in the other calendar and its Julian Day Number. ## Two calendars, and a jump The Julian calendar adds a leap day every fourth year, so its average year is 365¼ days, slightly longer than the year of the seasons. Over the centuries the dates slipped, and in 1582 Pope Gregory XIII's reform dropped ten days and changed the rule: century years are leap years only when they divide by 400, so 1700, 1800 and 1900 were not, but 2000 was. Countries changed at different times. Britain and its colonies waited until 1752, when Wednesday 2 September was followed by Thursday 14 September. The weekdays carried on as normal; only the dates jumped. Russia changed in 1918 and Greece in 1923. The [Julian–Gregorian converter](https://pastcrumbs.me/julian-gregorian-converter/) has the full table. ## Old Style years and dates like 1720/21 Until 1752 the legal year in England began on 25 March, so a date between 1 January and 24 March carried the previous year's number. Writers often gave both: 1 February 1720/21 is 1 February 1721 as we count today. This finder reads every year as starting on 1 January and tells you when a date falls in that window; the converter has a box for years copied straight from an Old Style document. ## What the Julian Day Number is Astronomers number days in one unbroken count from noon on 1 January 4713 BCE (in the Julian calendar), ignoring months and years. Each day has one number, whichever calendar a writer used, which makes it the safest way to compare dates. Every conversion on this site goes through it. ## Sources - Jean Meeus, *Astronomical Algorithms*, 2nd edition (Willmann-Bell, 1998), chapter 7, “Julian Day”: dates to and from Julian Day Numbers, and the day of the week. - H. F. Fliegel and T. C. Van Flandern, “A machine algorithm for processing calendar dates”, *Communications of the ACM* 11(10), 1968, p. 657 ([doi:10.1145/364096.364097](https://doi.org/10.1145/364096.364097)): used to check every conversion. - [Calendar (New Style) Act 1750](https://www.legislation.gov.uk/apgb/Geo2/24/23), legislation.gov.uk: England's year beginning on 25 March, the year 1752 beginning on 1 January, and 2 September 1752 followed by 14 September. - Royal Museums Greenwich, [Which years are leap years?](https://www.rmg.co.uk/stories/time/which-years-are-leap-years-can-you-have-leap-seconds): the Julian and Gregorian leap-year rules, and Britain's change in 1752. - Claus Tøndering, [Calendar FAQ: the Gregorian calendar](https://www.tondering.dk/claus/cal/gregorian.php): the 1582 reform and each country's switch dates, including Sweden's. ## More from the reading room Every tool names its sources. - [Julian–Gregorian converter](https://pastcrumbs.me/julian-gregorian-converter/): Old Style to New Style and back, with every country's switch date and the 10 to 13 days between them. - [Easter date calculator](https://pastcrumbs.me/easter-date-calculator/): Western and Orthodox Easter for any year, with Ash Wednesday, Good Friday, Ascension and Pentecost. - [Roman numeral dates](https://pastcrumbs.me/roman-numeral-dates/): Numbers and whole dates in Roman numerals and back, with older forms like IIII and MDCCCC explained. - [Historical timeline maker](https://pastcrumbs.me/historical-timeline-maker/): Events with BCE and CE dates, notes and era bands, scaled for you; print it or save it as SVG or PNG. - [Old money converter](https://pastcrumbs.me/old-money-converter/): Pounds, shillings and pence to decimal at the 1971 rate and back, with guineas, crowns and florins. ## Recommended Two free services for researching online. 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When a country moved to the Gregorian calendar it left out the dates in between: in Britain, 3 to 13 September 1752 never happened. The card also shows the weekday if your source used the other calendar, in case the date was written Julian or Gregorian after all. **Which reading should I choose?** Choose the country your document comes from to read the date as it was written there. Choose the Julian or Gregorian calendar if you already know which one the writer used, for example a date marked O.S. (Old Style) or N.S. (New Style). **Did the days of the week change in 1752?** No. Only the dates jumped: Wednesday 2 September was followed by Thursday 14 September, so the weekly cycle ran on unbroken. That is why a weekday written in a document can help show which calendar the writer was using. **Why are Japan and Turkey not in the list?** Neither used the Julian calendar. Japan moved from its lunisolar calendar to the Gregorian on 1 January 1873, and a Turkish law of 1925 made the international year count official from 1 January 1926. Dates in their older calendars are not converted here.