Getting Week Number within month time frame: why 13 and -5?

Do your weeks begin on Friday? If not, I'm not sure that function works.

Let's break it down for the 1st January 2022:

Day() will return 1 (i.e. the 1st day of January)
Weekday() would return 7 (Saturday) but moving this back by 5 days will return 2 (Tuesday)
So we then have (13+1-2)/7=1
Similarly, for the 2nd, 3rd, 4th, 5th, 6th we would have (13+2-3)/7=1, (13+3-4)/7=1, (13+4-5)/7=1, (13+5-6)/7=1, (13+6-7)/7=1

On the 7th, it will wrap around to give (13+7-1)/7 which is now =2. I assume this function was written to force new week numbers to start on a Friday.

WBD

Let me add also my explanation.
The function is planned for weeks (it's best visible for week 2,3,4) starting Friday / ending Thursday

The -5 (it could be as well +2 ! try it !) is used to get 7 (last day of given week) on Thursdays
(Have you noted that dat-5 is used as argument for Weekday function.)
Of course 7 is the largest value we can get from weekday so for any non-ending_of_week day we will get lower number. But never lower than 1 - which we wll get for Fridays

Lets look on a sum of some_number plus 1 minus 7 (one is for the first day of month, 7 is for the largest possible resuly of weekday - as said above) and we want it to be exactly 7 (because we will divide it by 7 and drop fraction part).

some_number + 1 - 7 = 7
so
some_number = 7 -1 + 7
=13

Hope it helps

So tomorrow (same as today, yestarday and the day before yesterday) is 5th week of June, then Friday, Sat, Sun is 1st week of July, and starting Mon, July th is 2nd week of July.

If so the function from first post is wrong. It shall read:

Please Login or Register  to view this content.

All the explanations why 13 and why for Sunday (not Thu in this case) it shall be 7 are still valid.

As an aside, you could do this with a formula and bypass the UDF:

Please Login or Register  to view this content.

WBD