Question: how do you subtract bc from ad?
Answer: For example, if you need to work out how many years are between January 1, 200 B.C. to January 1, A.D. 700 you add the BC and AD numbers. The calculation is 700 + 200, which equals 900 years. However, you still have to adjust for the absence of year 0. You do this by removing 1 from your answer, so 900 minus 1 is 899.