This year’s Compact Calendar added “automatic holiday calculation” when the year is changed in the Excel spreadsheet. Holiday calculations are terribly tricky, though, and a bug in the Easter Calculation was reported by Mike Kennedy with OpenOffice. The Easter calculation I’m using, he pointed out, assume date entry in a certain text format which is not universal. I went back and looked at it and saw he was right, though I couldn’t duplicate the other reported bug. Anyway, I’ve uploaded a more robustly-coded version of original Easter calculation, which substitutes the locale-specific date string with the Excel DATE function.
UPDATE: After downloading OpenOffice and cross-checking the calculation with Google Spreadsheet, it appears that the cause of the bug is due to a difference between in how the
DAY() function works for values under 61. So if you are using Excel you are fine, but OpenOffice users should probably use the
UPDATE2: Here’s an explanation of why Excel’s DAY() function is buggy; it was originally to maintain compatibility with Lotus 1-2-3, which used to be the dominant spreadsheet.
In Excel 2007, Easter appears to be calculated correctly for the next five years. If you are outside the USA, you can re-download the ZIP file from the Compact Calendar Page for the more robust version of the calculation.