Comprehensive Calculator Guide
This calculator counts the years between a BC year and an AD year correctly, allowing for the fact that the calendar has no year zero. From 500 BC to AD 2026 is 2,525 years, not 2,526. It also shows the BC year in the astronomical numbering astronomers use for calculation, and the span in centuries, for history students and anyone curious about ancient dates.
No year zero
Dionysius Exiguus numbered years from AD 1 in the sixth century; counting backwards before it spread in the eighth. So 1 BC is followed directly by AD 1, and adding the two years counts one too many: span = BC + AD − 1.
Astronomers since the 18th century use a year 0: 1 BC is year 0, 2 BC is −1, so the astronomical year = 1 − BC year, and plain subtraction works.
How to Use
- Enter the BC year, such as 500.
- Enter the AD year.
- Press “Work out the years” to see the span, the astronomical year and the centuries.
Formula Used
Span = BC year + AD year − 1 | Astronomical year = 1 − BC year
Practical Examples
- Example 1
- 500 BC to AD 2026: 500 + 2026 − 1 = 2,525 years, 25.25 centuries; 500 BC is astronomical year −499.
- Example 2
- 1 BC to AD 1: 1 + 1 − 1 = 1 year; 1 BC is astronomical year 0.
Important Tips
- Very old dates are often approximate.
- The first century runs from AD 1 to 100.
- Use the Hijri converter for dates after AD 622.
Common Mistakes to Avoid
- Adding the years without subtracting one.
- Subtracting a BC year as if it were AD.
- Mixing astronomical and historical numbering.
Frequently Asked Questions
- How many years from 1 BC to AD 1?
- One, as there is no year zero.
- How do I count across BC and AD?
- Add the years and subtract one: 300 BC to AD 200 is 499 years.
- BC/AD vs BCE/CE?
- Same years, different labels.