Changing when a month starts

Hi everyone

I’ve had a few ideas before coming here but they seem to have been addressed by other users except one

I’d like to be able to change where a month starts and ends as my salary doesn’t come in at exactly the end of the month. I end up having to look at different sets of monthly data to get a more accurate depiction of the month…you can spend a lot of money in 5 days!

Thanks!