Start with the right question
An invoice can be numerically correct while charging for work you did not agree to, or it can reflect agreed work with a simple calculation error. A line-by-line reconciliation helps identify which issue actually needs resolution.
Work through the checks
Identify the accepted baseline
Keep the quote, estimate, contract, and acceptance record. Note whether the document gave a fixed price or an estimate with stated conditions. Do not treat every preliminary quote as the final agreement.
List approved changes
Record additions, substitutions, delays, and changes to quantity or rate. Link each to a written approval or explain where the agreement is disputed. A later invoice is not itself proof that a change was authorized.
Check the arithmetic
Recalculate quantities, rates, taxes, credits, and payments. Separate refundable deposits from completed payments. Keep currency and billing periods consistent so the comparison does not create a false discrepancy.
Ask about the specific line
Identify the item, expected amount, billed amount, and supporting record. Request the provider's explanation. Preserve disputed and undisputed items separately without deciding payment obligations from this checklist alone.
A record you can use
- Invoice line
- Quoted or agreed basis
- Change reference
- Expected and billed amounts
- Explanation or dispute
Keep this record locally. Use document references rather than publishing account numbers or other people's personal details. An empty field means the information is still missing; it should not be filled with an AI guess.
Worked example
A fictional repair quote lists two hours at $80 and $40 in parts. The invoice lists three hours and $40 in parts. The customer identifies the $80 difference and asks for the additional-work authorization rather than claiming the entire $280 bill is an arithmetic error.
This example is fictional and illustrates the method, not a real case result.
Limits and next steps
This page does not determine whether an estimate is binding, whether work was authorized, or what you may withhold. Those questions depend on the agreement and applicable law.
Send a concise comparison with relevant copies and keep the response. If the disagreement involves legal rights or significant consequences, seek advice using the actual agreement and change history.