Convert Monthly values in to weekly and opposite.

The formula itself is pretty straightforward but the fact that # of weeks in a month isn't constant means you need to do your calculations based upon how many weeks are in the month/year you're talking about. Furthermore it is complicated by the fact that the beginning of the week may be in a different month than the end of the week.

In general, assume a weekly employee gets paid PW dollars per week. Then their monthly salary (MS) is PW * (paydays in Month). Weeks in month can be 4 or 5, depending on the month and where the payday actually falls. Determining that requires a calculation itself.

If you pay on Fridays then you count the # of Fridays in the month. The easiest way to do that is find the first Friday of the month and then keep adding 7 to the days until it rolls over to the next month. Example: July 4th was the first Friday of July 2025. July has 31 days so there are (4, 11, 18, 25) paydays in July 2025, or 4. Getting the first X of a month can be done by getting the first day of the month (e.g. 7/1/2025) and then checking the DayOfWeek. Find the # of days from the 1st to Friday to get the # of days you need to move forward. Example: July 1 2025 was Tuesday. Diff(Tuesday, Friday) = 3 days so the first Friday is 1 + 3 = 4. But Nov 1st 2025 is a Saturday. Diff(Saturday, Friday) = 6 days so Nov 7th 2025 is the first Friday.

Can all this be done in a simple equation/expression? Yes but I wouldn't recommend it. I would recommend that you create one or more helper functions in Excel to do the calculations. Then use them in your expression(s).

For monthly employees the same information is needed but you go the other way. Let's write the final formula. MS = PW * (paydays in Month). So given a monthly employee the PW = (MS / (Weeks in Month).

The only concern I'd have with these kinds of calculations is that saying how much did someone get paid in, say, July, isn't going to be correct necessarily because the month could roll over during the pay week so they got a full paycheck but some was for last month and some for this month. If you want more granular control then you might need to consider calculating based upon pay per day * # of days in month. That gives you a more accurate value for weekly folks but monthly folks have a variable rate pay per day (because the # of days in a month varies).