Thank you for the replies. This is the first time I've posted anything and I'm impressed with the willingness to help. I've chased down several rabbit holes and your responses reinforce how complicated a mathematical approach to this problem would be for someone like me who is not very skilled in this area. I changed by approach. My project only needs 10 years worth of Ethiopian dates with matching Gregorian dates. I created a table using an online date converter (one date at a time) of where Ethiopian leap years fell and Gregorian leap years fell. Then I started with the first Ethiopian date of our data collection period and found the matching Gregorian date. Then I created one year's worth of corresponding dates. I use a very flexible editor so this took me about and hour. I allowed for 12 months of 30 days and 1 month of 5 days (6 if leap year) for the Ethiopian side and the regular Gregorian months with their unique number of days for the Gregorian side. As I built each additional year, I watched for leap years on both sides. The whole process took me about 5 hours including checking. I created several thousand records in a text file of two variables, an Ethiopian date and a Gregorian date. I have that data available as a SAS data file that I can sort depending on which date I need to match. This allows me to have the Ethiopian date AND the Gregorian date defined as a SAS date in my code. I can add the number of days I want to the Gregorian date and then look up the Ethiopian date that matches the Gregorian date. While I know this is not a very elegant solution, it's working for me.     ... View more