When the extended amount does not match quantity times unit price
A line on your vendor's invoice reads 24 at 12.50. The extended amount printed beside it is 270.00.
Twenty-four times 12.50 is 300.00. So the extended amount does not match quantity times unit price. Something has to account for the missing 30.00.
Almost always, nothing is wrong and your vendor is right. Four ordinary things account for most of these gaps. None of them is an error.
Four reasons the extended amount does not match
A discount applied to the line
The unit price stays at list. The discount sits in its own column, or in the description, or nowhere on the page at all. The extended price is the one you owe.
Both numbers are correct and they disagree on purpose. Whoever keys this line has to take the extended price, not the product.
A price break the line does not reprint
Bracket pricing drops the rate once the quantity crosses a threshold. Some vendors reprint the unit price at the break rate. Many print list and bill at the break.
That second habit is the gap you are looking at. It also moves, because the break depends on how much was ordered that day.
Pricing per thousand
Tags, labels, corrugated, wire and fasteners are often priced per M. The unit of measure carries the divisor. The quantity column does not.
Multiply the two numbers as printed and you are out by a factor of a thousand. This one is easy to spot precisely because it is so large.
A charge folded into the line
A broken-case fee, a small-order charge or a per-line handling fee sometimes lands inside the row. The extended price then carries something the unit price never had.
A credit memo is not a failed line either
A credit memo prints the quantity and the unit price as positives. The extended amount comes back negative, in parentheses or with a minus sign.
Compare the signed numbers and every line of every credit memo fails. Compare the magnitudes and the line is exactly what it looks like. Correct.
So the check here compares magnitudes: 92.50 against 92.50, sign set aside. Sign is not going unchecked. A separate check reconciles the signed document total against the signed lines, so a row with the wrong sign still fails there.
How close counts as matching
Exact equality is the wrong test. Fractional quantities produce fractions of a cent, and two systems will round them in two directions.
So there is a tolerance, and it is proportional as well as absolute. It is the greater of two cents and half of one percent of the line.
A penny on a 4.15 line is a real discrepancy. A penny on a 41,500 line is rounding. One flat threshold cannot be right for both.
Run the check yourself
The same function the gate calls. Change any number.
- Quantity x unit price
- 300.00
- The line says
- 270.00
- Difference
- 30.00
- Tolerance on this line
- 1.35
This line is marked. The document waits for a person. The check cannot tell a discount from a transposition, so it does not guess which one this is.
Ten percent off the line. The unit price stays at list, so the row will not multiply out.
Reading the gap to work out which one you have
The size and shape of the difference usually names the cause outright:
- The gap is a round percentage of quantity times unit price. That is a discount or a price break.
- The extended price is a thousandth of quantity times unit price. That is per-M pricing, read literally.
- The same flat amount is missing from several rows. That is a per-line fee, not an arithmetic fault.
- The magnitude matches and only the sign differs. That is a credit.
- The digits are the same in a different order. That is a transposition, and it is worth somebody's attention.
That last one is the case the check exists for. It might be your vendor's arithmetic. It might be somebody reading the row wrong, including us.
What happens to a line that does not multiply out
The row is marked, and the reason is printed next to it. Not “line 7 failed”.
You get the arithmetic that was expected, the amount your vendor actually printed, and the note that a discount or a price break would explain the gap.
Then the document goes to a person. Nothing reaches a CSV or a sheet until every check on that document has passed.
Read the four reasons again, because this is the honest cost of that rule. An invoice with a discount column has a gap on every row of the page.
So it is a page somebody will look at. What the check buys you there is the reason printed beside each row, rather than forty rows and no explanation.
How much that costs depends on how many of your vendors bill that way. That is a question about real documents, and the honest answer today is that we have not measured it on yours.
What a gap does not tell you
It needs all three numbers printed on the row. Freight lines, subtotals and description-only rows have nothing to multiply, so they are marked as non-item rows and skipped.
And it never says who was wrong. It says the two numbers on that row disagree by more than rounding. Which one to trust is a judgement, and a discount column usually answers it in a second.
Run it on a page off your own desk
Take a vendor invoice with a discount column on it and drop it in here. Every line comes back with quantity, part number or SKU, unit price and extended price. Anything that does not multiply out is marked. Nothing is stored and there is no sign-up.