Add Formula to Amount

Hello, this is my first post...so excuse me if I don't explain my problem good enough. I have a page where one can input an amount in a given field to a specific user. So I would type in a specific user and enter an amount that user has paid and the date the amount was paid. But on the report page, I would like to have a field that shows how much the user has paid in a specific amount of time (week, month, or year). Is this something that can be done?