I need a NON-negative function to add to my subtotal; HOW?

[arrow]

The title says most of it: "I need a NON-negative function to add to my subtotal; HOW?"

Here's the details:
I'm doing a running subtotal of my traveling expenses. I'm able to add up my expenses that are OVER $39 a day. So, I've got a math function that adds up the expenses and deletes $39 from them. PROBLEM: I can't end up with a negative value.

Example:
Day One: $149 - $39 = $110 this one's OK
Day Two: $0.53 - $39 = -$38.47 WRONG WRONG WRONG... I need a value of ZERO for this subtotal.

How do I do this?

LP

p.s.: This is the third time I've posted this message. Please excuse the repeated postings. I can't tell which section is most likely to get me the answer.

[acknak]

[I removed the other two: never post duplicates; when in doubt, use the more generic forum]

Try this:
A1: $$ for one day
B1: =IF(A1>39;A1-39;0)

That will give you the allowable expenses for one day. Then add those together for the subtotals.