Progressive Addition

I want to figure something out in Excel 2000, but I've been trying different things for hours and I can't find it. I want to do progressive addition - if a certain condition is met, I want to add a certain amount to an existing amount and have it stay that way. I'm trying to create a budget tracking program in excel and I want to have it add a certain amount to the budget category each Sunday. I tried using the IF function, but it always creates a circular reference. Anyway, I can get it to display whether it is sunday, but I can't figure out how to make it add. I basically just want to do a simple if/then function:

If B3 = Sunday
Then add 50 to C5

Does that make any sense? Is there any way to do that?

Thanks.

Hello

See attached file and formula in green coloured cell.

Hope this will help u.

Thanks. That helped a lot. Guess the way I was thinking of it just didn't work, eh? But still, a way to get it done, that's what I needed.

Thanks,
FrizbeeFanatic14