Roman Calendar Converter
Convert a Gregorian date to Kalends / Nones / Ides notation and AUC year.
Overview
The Roman Calendar Converter renders any Gregorian date in the notation used by ancient Romans, anchored to the three named days each month: the Kalends (1st), the Nones (5th or 7th), and the Ides (13th or 15th). It also reports the year using the AUC (ab urbe condita, "from the founding of the city") era counted from the traditional founding of Rome in 753 BC.
Useful for Latin students translating classical texts, historians dating Roman inscriptions, fiction writers building authentic ancient-world settings, museum curators labelling artefacts, and anyone who has wondered what date "the Ides of March" actually refers to (the answer is March 15).
How it works
The Roman month was divided by three reference days. The Nones fell on the 7th in March, May, July, and October ("Mars, May, July, October the Nones the seventh day be"), and on the 5th in the other months. The Ides followed eight days after the Nones — the 15th in those four months and the 13th elsewhere. All other dates were named by their count backward to the next reference day, inclusively counted.
The AUC era starts from the traditional founding of Rome in 753 BC according to Varro's chronology, so a Gregorian year Y maps to AUC Y + 753 (with no year zero in either system). The Roman calendar itself underwent several reforms — this converter uses the post-Julian (45 BC) layout that matches the months and lengths of the modern Gregorian calendar.
Examples
44 BC March 15 → Idus Martiae, AUC 710 (death of Julius Caesar)
2026-05-18 → a.d. XV Kal. Iun., AUC 2779
2026-01-01 → Kalendae Ianuariae, AUC 2779
2026-07-04 → a.d. IV Non. Iul., AUC 2779
FAQ
Why is everything counted backward?
Roman day-naming worked from the next upcoming Kalends, Nones, or Ides. The day before the Ides of March was pridie Idus Martias; two days before was ante diem III Idus Martias (inclusive count, so III not II).
What does "a.d." mean here?
Ante diem — "before the day." a.d. III Non. Mai. means "the 3rd day before the Nones of May," which is May 5 (inclusively counted from the Nones on May 7).
Why is the AUC year sometimes off by one?
Different ancient sources placed Rome's founding in slightly different years (Varro's 753 BC is the most common, but Cato gave 752 BC, Polybius 750 BC). This tool uses Varro's date.
Was Caesar killed on the 15th or the 14th?
The 15th. The Ides of March fall on the 15th (not the 13th) because March is one of the four months with a late Ides.
Does it use the Julian or Gregorian calendar for old dates?
The tool maps Gregorian dates to Roman notation. For inscriptions earlier than AD 1582, the proleptic Gregorian date may differ from the Julian date by up to two weeks — for that case, use the Julian date converter.