Calculations by Dates

Hello,

I'm wondering if it's possible to do calculations by dates. I'm looking at doing a budget database and I would need calculations to be done by the month.

My current structure is 1 table, "Budget Allowances" that has the amount of money that can be spent in various areas, food, gas, rent, entertainment ... I have a second table, "Expenses." On this table you enter all expenses and select what type of expense it is (from a value list of the areas)

What I am looking to do is have a summary page where it takes an amount from "Budget Allowances" and substracts amounts from "Expenses" labeled for that particular area.

Ex: Budget Allowances::Entertainment - Expenses:(any field that has been labeled entertainment expense)

I need some help here. My problem is how to distinguish the fields labeled as entertainment. So it doesn't substract gas from entertainment for example.

The other thing I'm looking for is to have it reset by month. So when the first of the month rolls around it starts again. Throughout the month you could see what your current balance is but then resets at the beginning of the month. In the end it would do the calculation based on date.

However I would like to store the final amount spent at the end of the month. That way I could have a layout that shows spending over the last few months or years.

If anyone has any ideas it would be a big help.

Thanks

js22