daily/weekly budget calculation (if cell1 is less than 0 take X from cell2)

I am trying to create a formula for a budget.
example:
I have a daily budget of $20
I also have a weekly budget of $100

So If I spend more than $20 in a day I want the amount subtracted from the $100 weekly budget. But I don't want the remainder added to the weekly budget.

So if on Monday I spent $40, the weekly amount would show $80, On Tuesday I spent $10 the weekly would still show $80.

So the weekly amount never increases, it only decreases if the daily budget goes into negative numbers.

If Monday to Sunday are in cells A1:A7 with the daily spend in B1:B7, your weekly budget cell would need to be something along the lines of:

=100-if(B1>20,B1-20,0)-if(B2>20,B2-20,0)-if(B3>20,B3-20,0)-if(B4>20,B4-20,0)-if(B5>20,B5-20,0)-if(B6>20,B6-20,0)-if(B7>20,B7-20,0)

or you could add an extra column to show how much over the daily budget you have gone, sum that up and subtract from 100

C1=if(B1>20,B1-20,0), all the way down to C7

then weekly budget = 100-sum(C1:C7)

Hope that helps.

Thank you very much guys. That solved my problem!