How to Convert a Date to Gregorian Value
- 1). Truncate the digits to the right of the hundreds place in the year in question. For example, for the year 1500, just look at the 15.
- 2). Multiply the result of Step 1 by 0.75.
- 3). Subtract 1.25.
- 4). Truncate any decimal points. This result is how many days to add to the Julian date that you are trying to convert to a Gregorian value. For example, December 1, 1215, has the calculation 12x.75-1.25 = 7.75. Truncating gives 7 days. So a Julian date of December 1, 1215, is December 8, 1215.
- 5). Handle BC dates the same way but subtract a year before doing any calculations. Then add the year back in at the end. The reason is to maintain the linear relationship of the formula, given that there is no 0 BC or 0 AD. 1BC was followed the next year by 1AD.
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