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Julian Date Converter
Convert any Gregorian calendar date into its Julian Day Number, or turn a Julian Day Number back into a calendar date. The Julian date converter also shows the day of the week and the matching date in the Julian calendar, so one lookup answers every version of the question at once.
| Gregorian date | 8 November 2026 |
| Julian Day Number | 2,461,353 |
| Day of the week | Sunday |
| Julian calendar date | 26 October 2026 |
How it works
A Julian Day Number counts days without stopping. It starts at noon on 1 January 4713 BC in the Julian calendar, which astronomers call Julian Day 0, and every day since then adds exactly one. That single unbroken count is what makes the system useful: dates that look messy in month-and-year form become plain numbers, and the distance between two dates is a subtraction.
To convert a date, enter the year, month, and day, then press Convert. The tool checks that the date is real — it will not accept 31 April or 29 February in a year that is not a leap year — and then applies the standard conversion formula. The result appears as the big number, with the day of the week and the Julian calendar date underneath. Switch the direction to "Julian Day Number → Gregorian date" and the tool runs the same calculation in reverse: type a whole Julian Day Number and it returns the calendar date it belongs to.
The day of the week comes straight from the Julian Day Number, because the seven-day week lines up neatly with it: the remainder when the number is divided by 7 tells you the weekday, with a remainder of 0 meaning Monday and 6 meaning Sunday. The Julian calendar date is the same day read in the older calendar system, which runs 13 days behind the Gregorian calendar between 1 March 1900 and 28 February 2100. So 8 November 2026 in the Gregorian calendar is 26 October 2026 in the Julian calendar.
Astronomers, historians, and software developers all use Julian Day Numbers for the same reason: they remove every quirk of the calendar. Months have different lengths, leap years break the pattern every four years, and calendar reforms moved dates around — but a day count has none of that. If you are working out the gap between two events, dating an old observation, or storing dates in a database where sorting must be simple, converting to Julian Day Numbers first makes the arithmetic trivial.
Worked example
Take 8 November 2026 and convert it step by step.
Step 1: The month is 11, so a = ⌊(14 − 11) / 12⌋ = 0. That gives y = 2026 + 4,800 − 0 = 6,826 and m = 11 + 0 − 3 = 8.
Step 2: The month term is ⌊(153 × 8 + 2) / 5⌋ = ⌊1,226 / 5⌋ = 245.
Step 3: The year term is 365 × 6,826 = 2,491,490, plus ⌊6,826 / 4⌋ = 1,706, minus ⌊6,826 / 100⌋ = 68, plus ⌊6,826 / 400⌋ = 17.
Step 4: Add the day and the constant: 8 + 245 + 2,491,490 + 1,706 − 68 + 17 − 32,045 = 2,461,353.
The tool shows the same result: Julian Day Number 2,461,353. Dividing 2,461,353 by 7 leaves a remainder of 6, which means Sunday, and the Julian calendar date is 26 October 2026. To check the reverse direction, enter 2461353 with the direction set to "Julian Day Number → Gregorian date" and the tool returns 8 November 2026.
FAQ
What is a Julian Day Number?
A Julian Day Number is a continuous count of days starting from noon on 1 January 4713 BC in the Julian calendar. Each day adds exactly one to the count, so 8 November 2026 is Julian Day Number 2,461,353. Astronomers use it because it turns any date into a single number, which makes the gap between two dates a simple subtraction instead of a calendar puzzle.
Is the Julian Day Number the same as a date in the Julian calendar?
No, they are two different things that share a name. The Julian Day Number is a day count used mostly in astronomy. The Julian calendar is the older calendar system that the Gregorian calendar replaced, and it is still used by some churches. This converter shows both: the Julian Day Number and the matching date in the Julian calendar.
Why does the Julian Day start at noon instead of midnight?
Astronomers of the past did most of their observing at night, so starting the day at noon kept a whole night of observations inside a single numbered day. The convention stuck. For everyday converting, the whole-number Julian Day Number for a date is the value at noon on that date, which is the standard civil-date value this tool uses.
What dates can this converter handle?
The converter works for Gregorian dates from 1 January 1600 through 31 December 2400, and for Julian Day Numbers in the matching range. Dates before the Gregorian calendar was adopted in 1582 are shown with the proleptic Gregorian calendar, which extends the modern rules backwards, so very old dates may differ from what a historical record calls them.
How do I find the number of days between two dates with this tool?
Convert each date to its Julian Day Number and subtract the smaller one from the larger one. For example, 1 January 2026 is Julian Day Number 2,461,042 and 8 November 2026 is 2,461,353, so the gap is 311 days. That is the whole point of the system: date differences become plain subtraction.