BC & AD Date Calculator
Measure the interval between BCE and CE dates using an explicit Gregorian or Julian calendar. Compare calendar days, weeks, years, and months across eras.
Your results
Enter two dates to see elapsed days and a calendar breakdown.
Days = end day number − start day number, using the proleptic Gregorian calendar. A Julian day number is a continuous day count, distinct from the Julian calendar.
1 BC is followed by 1 AD, with no year zero in the entered dates. Calendar durations count from the earlier date and clamp at month ends. Gregorian leap years are divisible by 4, except centuries not divisible by 400.
How to use BC & AD Date Calculator
- Enter each date using a positive year and select BCE or CE.
- Choose the proleptic Gregorian or Julian calendar for both dates.
- Calculate the signed day difference and calendar-unit breakdown.
What is BC & AD Date Calculator?
Historical dates need both an era and a calendar convention. This calculator extends the selected Gregorian or Julian rules across the whole interval. It does not switch calendars at a historical reform date. The civil labels move directly from 1 BCE to 1 CE; year zero is not accepted as a user-entered year.
- BCE-to-CE intervals without a civil year zero
- Explicit Gregorian or Julian calendar rules
- Day counts and calendar-unit breakdown
- Leap-year validation within the selected calendar
A practical example
December 31, 1 BCE → January 1, 1 CE Same selected calendar, end date excluded
1 calendar day
Frequently asked questions
Which calendar is the default?
The default is proleptic Gregorian: Gregorian rules extended through all supported years. You may explicitly choose Julian rules instead.
Does the calculator model a country's calendar reform?
No. Real adoption dates varied between places. Both dates use the single selected calendar, with no automatic gap or jurisdiction-specific reform.
Why is year zero rejected?
Civil BCE/CE numbering has no year zero. Internal arithmetic can use an astronomical year mapping, but dates shown to you always use positive years with BCE or CE labels.