↑↓ to move · Enter to open · Esc to close

BC to AD Calculator

Count the years between two dates on either side of the BC and AD boundary. The BC to AD calculator handles the missing year 0, which trips up most mental math.

Runs in your browser. Your data is not uploaded.
Built by · Updated
From

To

Years between
–

How to use the BC to AD Calculator

  1. Enter the From year and pick BC or AD.
  2. Enter the To year and its era.
  3. Press Calculate. The number of years appears, with the astronomical year numbers used.

How it works

astronomical year = 1 − BC year   (1 BC = 0, 2 BC = −1)
astronomical year = AD year
years between = astronomical(to) − astronomical(from)

The calendar goes straight from 1 BC to AD 1. Astronomers renumber BC years so that 1 BC is year 0, which makes subtraction work.

Examples

  • 500 BC to AD 2026: 2026 − (−499) = 2,525 years, not 2,526.
  • 1 BC to AD 1: 1 year.
  • The founding of Rome in 753 BC to the fall of the Western Roman Empire in AD 476: 1,228 years.

BC, AD, BCE, and CE

BCE (Before Common Era) and CE (Common Era) use the same numbers as BC and AD. Only the labels differ, so 500 BCE is the same year as 500 BC.

Counting years across BC and AD by hand

When one date is BC and the other is AD, add the two year numbers and subtract 1. The 1 comes off because there is no year 0 between 1 BC and AD 1. From 44 BC to AD 2026 that is 44 + 2026 − 1 = 2,069 years. From 3000 BC to AD 2026 it is 5,025 years.

When both dates are BC, subtract the smaller number from the larger, because BC years count down toward AD 1. From 500 BC to 300 BC is 200 years. When both are AD, subtract as usual.

The missing year 0 also explains why centuries and millennia start on a year ending in 1. The 1st century AD ran from AD 1 to AD 100, so the third millennium began on 1 January 2001, not in 2000. The 1st century BC ran from 100 BC to 1 BC.

Where the BC and AD labels come from

AD stands for Anno Domini, Latin for "in the year of the Lord". BC means "before Christ". The system was worked out by the monk Dionysius Exiguus in AD 525 and spread through Europe over the following centuries. Because it was set up before the number zero was used in Europe, it starts at 1 in both directions.

Limitations

  • Counts whole calendar years. It does not account for months or the Julian-to-Gregorian change.
  • Historical dates before about the 1st century BC are often approximate.

Frequently asked questions

Is there a year 0?

No. In the BC/AD system, 1 BC is followed directly by AD 1.

How many years between 44 BC and AD 2026?

2,069 years.

Why is the answer one less than adding the numbers?

Because adding counts a year 0 that never existed.

How many years ago was 500 BC?

In 2026, 500 BC was 2,525 years ago: 500 + 2026 − 1.

What do BC and AD stand for?

BC means "before Christ" and AD stands for Anno Domini, Latin for "in the year of the Lord". BCE and CE use the same numbers with neutral labels.

Often used together with BC to AD Calculator.