BC to AD Converter

Frequently asked questions

Why is there no year 0?

The BC/AD system was introduced by Dionysius Exiguus in 525 AD, long before zero was widely used as a number in Europe. The calendar simply jumps from 1 BC straight to 1 AD, so subtracting a BC year from an AD year without correcting for the missing zero gives an answer that is one year too large.

What is astronomical year numbering, and when should I use it?

Astronomical year numbering inserts a year 0: 1 BC becomes year 0, 2 BC becomes year -1, and so on (astronomical year = 1 - BC year). AD years are unchanged. Use it whenever you do arithmetic across the eras, because then plain subtraction works: 2026 - (-43) = 2069 years between 44 BC and 2026 AD.

How many years are there between 44 BC and 2026 AD?

2069 full years. 44 BC is astronomical year -43, so 2026 - (-43) = 2069. The naive calculation 44 + 2026 = 2070 is a common off-by-one error caused by forgetting that there is no year 0.

Is BC the same as BCE, and AD the same as CE?

Yes. BC (Before Christ) and BCE (Before Common Era) use identical numbering, as do AD (Anno Domini) and CE (Common Era). BCE and CE are the religiously neutral labels preferred in academic writing; the numbers are exactly the same.

Why does this tool refuse a year 0 input instead of guessing?

Because a year 0 does not exist in historical BC/AD numbering, silently mapping it to 1 BC or 1 AD would corrupt every elapsed-year calculation by a full year. The tool stops and explains the two real neighbors instead of guessing.