A second calculation pass catches the errors that are easy to miss when you are close to the work. Use a calculator or spreadsheet, then compare the result with the invoice line by line.
Check quantities and units first
Confirm that the quantity on the invoice matches the work delivered and that the unit is consistent. Two hours is not the same as two days; a pack of ten is not the same as ten individual items.
Recalculate every line total
Multiply quantity by rate for each line. Round only in the way your invoice or accounting process requires, and keep the same precision across the document.
| Line | Calculation | Expected total |
|---|---|---|
| Consulting | 6 × 75.00 | 450.00 |
| Template pack | 2 × 40.00 | 80.00 |
| Subtotal | 450.00 + 80.00 | 530.00 |
| Discount | 530.00 − 30.00 | 500.00 |
Check adjustments and the amount due
A discount, credit or tax line should make the arithmetic traceable. Recalculate the amount due from the subtotal, not from a previous total that may already include an adjustment.
Use a second-pass routine
- Read the invoice from bottom to top so you do not simply repeat the first pass.
- Recalculate each line with a separate tool.
- Compare the invoice total with the sum of the line totals.
- Check the amount in words, if your invoice uses one, against the numeric amount.
- Open every payment link and confirm it points to the intended recipient.
Common calculation mistakes
- A quantity typed as text, so the spreadsheet does not multiply it.
- A rate entered in a different currency from the line total.
- A discount subtracted twice, or not reflected in the amount due.
- A tax rate applied to the wrong base or copied from an old invoice.
What this check does not cover
Arithmetic correctness does not establish tax compliance, contract compliance or payment receipt. Confirm tax treatment and invoice requirements for your jurisdiction, and reconcile the payment separately.
Read how to fill out an invoice first if you are still assembling the document.