Julian Period year
A year number from 1 through 7,980.
Scaliger’s 7,980-year cycle
Current Julian Period
Cycle Year
Enter a year on either side. The other side updates automatically using only the Julian calendar—never the Gregorian calendar.
Julian calendar year
BC or AD, with no year zero.
Cycle Combination
Choose one number from each cycle. The corresponding period and calendar years update above; the Dionysian epact and dominical letter appear below.
Dionysian epact: 12
Dominical letter: E
How the conversion works
Scaliger’s Julian Period combines three repeating cycles: the 15-year indiction cycle, the 19-year lunar cycle, and the 28-year solar cycle. Because 15, 19, and 28 are pairwise coprime and their product is 7,980, every possible combination occurs exactly once in a Julian Period.
Julian Period year 1 is Julian calendar year 4713 BC, and year 7,980 is 3267 AD. The converter uses the proleptic Julian calendar throughout; it does not use Gregorian dates. Internally, the year conversion is:
astronomical year = Julian Period year − 4713
Astronomical year 0 corresponds to 1 BC, −1 to 2 BC, and +1 to 1 AD. The displayed calendar therefore uses ordinary BC/AD notation and has no year zero.
For Julian Period year Y, each cycle position is ((Y − 1) mod cycle length) + 1. The three positions together identify one unique year from 1 through 7,980.
The Dionysian epact is determined by the 19-year cycle: 11 × (19-year cycle − 1) mod 30. A remainder of zero is the nulla epact in Dionysius; this converter displays it as 0.
The dominical letter is determined by the 28-year solar cycle. The letters A–G mark successive dates beginning with A on 1 January; the dominical letter identifies the dates that are Sundays. Julian leap years have two letters, one for the part of the year before the leap-day adjustment and one for the part after it.
The 15-year indiction cycle does not alter the epact or dominical letter; it completes the three-cycle combination that makes the Julian Period unique.