Invoice math
How can I check an invoice’s math automatically?
Last updated
Recompute the invoice from its own figures: each line’s quantity times price, the lines against the subtotal, the tax against its printed rate, and the total. InvoiceParser Pro’s free invoice math checker does all four for up to 3 invoices a day with no sign-up and tells you in plain words which line or total is off and by how much; a workspace runs the same check on every invoice it reads. For a few invoices a month, a spreadsheet with four formulas does the same job, as long as you type the figures correctly.
Without IPP
Check the math in a spreadsheet
- 1
Type the lines
One row per line: quantity in B, unit price in C, and the line amount printed on the invoice in D.
- 2
Check each line
In E2 enter =B2*C2-D2 and fill it down. Anything other than zero (allowing a cent for rounding) is a line that does not add up.
- 3
Check the subtotal
Compare =SUM(D2:D20) with the printed subtotal. =SUMPRODUCT(B2:B20,C2:C20) gives the subtotal the quantities and prices imply.
- 4
Check the tax
Multiply the taxable amount by the printed rate, for example =D22*0.15 for South African or Namibian VAT at the standard rate, and compare it with the tax printed. A mixed invoice needs this per rate.
- 5
Check the total
Subtotal, less any discount, plus shipping, fees and tax, must equal the printed total. Query any difference before paying.
- The check is only as good as your typing: a misread figure makes a correct invoice look wrong, or a wrong one look right.
Checked against Microsoft: SUMPRODUCT function, read 4 October 2026. Menus change; the vendor's page is the authority.
In InvoiceParser Pro
Use the free invoice math checker
- 1
Open the checker
Go to the invoice math checker. There is no account to create and no card; up to 3 invoices a day are free.
- 2
Drop the invoice
Upload a PDF or a phone photo. The invoice is read, then every line, the subtotal, the tax and the total are recomputed from the invoice’s own figures.
- 3
Read the verdict
You get one plain sentence: everything adds up, or which line is off and by how much, or how far the lines are from the subtotal. The page is shown beside it so you can compare.
- 4
Download the figures
Take the invoice as Excel, with every line item, or as CSV. To check every invoice as it arrives, open a free workspace: 25 invoices a month, each checked the same way.
How reliable is an automatic check?
An automatic check recomputes what was read, so a misread figure is the main risk: the checker can flag a correct invoice, or pass one whose wrong figure was read as right. Each field IPP reads is scored High, Medium or Low confidence so you know which figures to look at.
In IPP’s own benchmark (181 synthetic test documents, run through live production on 3 October 2026), all 5 of the 5 invoices whose printed figures did not add up were flagged, and 2 of the 172 documents that did add up were flagged anyway, both severely blurred photos that were misread. The method and every miss are on the accuracy page. It is a test set, not your invoices.
What a math check cannot tell you
An invoice can add up perfectly and still be wrong to pay. A math check does not tell you:
- whether the price is the one you agreed with the supplier;
- whether the goods arrived or the work was done;
- whether you have already paid this invoice (a duplicate check does that);
- whether the VAT rate printed is the right one for the supply, only whether the VAT matches the rate printed.
What IPP does not do
- The free checker without an account does not check for duplicates; a workspace does.
- It does not compare prices with a quote, a contract or an agreed rate.
- When a page prints several percentages, such as fee percentages beside the VAT, it checks that the totals add up but does not test the VAT against a rate.
- Up to 3 invoices a day on the free checker; more needs a free workspace or a plan.
Questions
What does an invoice math check look at?
That each line’s quantity times price equals its amount, that the lines add up to the subtotal, that the subtotal less discount plus shipping, fees and tax equals the total, and that the tax matches the printed rate.
Is there a free tool to check invoice math?
Yes. InvoiceParser Pro’s invoice math checker checks up to 3 invoices a day with no account and no card, and lets you download the figures as Excel or CSV.
Can I check an invoice’s math in Excel?
Yes: =B2*C2-D2 for each line, SUM against the subtotal, the taxable amount times the rate against the tax, and the total. It works if you type every figure correctly.
What happens when an invoice does not add up?
The checker names the line or total that is off and by how much. In a workspace the invoice is flagged with the exact difference and waits for a person to review it.
Does it check the VAT rate is legally right?
No. It checks the VAT against the rate printed on the invoice. Whether that rate applies to the supply is a tax question for you or your accountant.
Try it on one of your own invoices
Upload a PDF or a phone photo on the free tool, with no account (up to 3 invoices a day), and download the result as Excel or CSV. When you want more: the free plan reads 25 invoices a month; the 14-day trial gives you 50 invoices and the QuickBooks, Xero and Zoho Books push, with no card.