Many shops apply the diagnostic fee toward the repair when the customer goes ahead. Subtract the already-paid fee from the repair total and you get the balance still owed.
A $220 repair with a $75 diagnostic already paid leaves a $145 balance due — the fee is credited, not double-charged.
The example
Three jobs with the repair total and the diagnostic fee already collected.
| A | B | C | D | |
|---|---|---|---|---|
| 1 | Job | Total repair | Diagnostic paid | Balance due |
| 2 | Washer | $220 | $75 | $145 |
| 3 | Fridge | $340 | $89 | $251 |
| 4 | Dryer | $160 | $75 | $85 |
The formula
A single subtraction credits the fee:
How it works
The fee already paid comes off the final bill:
B2is the full repair price — parts and labor.C2is the diagnostic fee the customer already paid up front.- Subtracting credits that fee toward the repair, leaving the balance still due.
If your policy only credits the fee above a threshold, guard it with =B2-MIN(C2,Cap).
Try it: interactive demo
Enter the repair total and the diagnostic fee paid.
Variations
Cap the credit
Credit only up to a set amount of the diagnostic fee.
No credit if declined
If the customer declines the repair, the fee stands and nothing is credited.
Pitfalls & errors
Make the credit policy clear on the invoice — customers expect the diagnostic to come off once they approve the repair.
Do not let the balance go negative on a cheap repair; floor it with =MAX(B2-C2,0) if the fee can exceed the repair.
Practice workbook
Frequently asked questions
What if the customer declines the repair?
Can the balance go negative?
Stop fighting formulas. Learn them in a day.
This recipe is one of hundreds of real-world formulas we teach. Our Excel Formulas & Functions class covers lookups, logic, text, and dynamic arrays hands-on — live in Dallas–Fort Worth, Houston, Austin, Oklahoma City, Denver, or online.
See the Formulas & Functions Class