Is there any pracitcal difference between the two? Only I have now covered my spreadsheet with the other formula.

Unfortunately I have a new, related, question. I would now like to do the same thing, but for months. Because the difference in days means that one formula will end up missing a day here and there. Originally I was going to just do every 4 weeks but my boss would like it to be calender months, alas...

So, it's the same idea, to SUM all the numbers within a range that is flexible (thus takes the start date and keeps adding numbers until it reaches the last date of the same month).

Thanks again