📜 BC to AD Calculator
Enter two years, each marked BC or AD, to find out exactly how many years apart they are.
What this calculator does
The BC to AD Calculator finds the exact number of years between two dates, even when one or both fall before the Common Era (BC) and the other falls after it (AD).
How the calculation works
Calendar years have a quirk: there is no year zero, so 1 BC is immediately followed by 1 AD. To calculate correctly, each year is first converted into astronomical year numbering, where 1 BC becomes year 0, 2 BC becomes year -1, and so on, while AD years keep their normal value. Subtracting the two astronomical years gives the true number of years between them.
This tool is for general historical and educational reference. It uses the proleptic Gregorian calendar convention common in modern astronomy and history writing.