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Invoice approval and coding stamps for accounts payable
5 September 2026 ยท Estamplab
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An invoice coding stamp is the block a finance team presses on the top corner of a supplier invoice so that the invoice carries its own history: when it arrived, which account it belongs to, who approved it, and when it was paid.
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It is the cheapest internal control most finance teams own. It is also the one most often designed badly, because it gets drawn once by whoever ordered it and then used for a decade.
What goes on an invoice coding stamp
The useful ones carry five or six fields and nothing else. Every extra line is a line somebody has to skip past a hundred times a week.
- Received, with the date. This is the field that settles disputes about payment terms, because terms run from receipt and nothing else records it.
- GL code or account code, with enough room for your longest code. Measure your longest one before you order.
- Cost centre or department, if your chart of accounts uses one.
- PO number, where the business runs on purchase orders.
- Approved by, a blank line for initials rather than a name, because the approver changes.
- Date paid, or a separate PAID stamp if payment is a different desk.
What to leave off: the company name, which is already on the letterhead of everything else in the file, and the year, which will be wrong in January.
Approval stamp or coding stamp
They are usually the same block and people search for both, but the emphasis differs.
An approval stamp is about authority: who signed off, at what level, on what date. In a business with delegated spending limits the approval line is the control, and an initial in a box is what an auditor follows.
A coding stamp is about where the cost lands: the GL account, the cost centre, the project. It is a bookkeeping instrument rather than an authority one.
Most teams want one block that does both, which is why the standard layout is a grid of labelled boxes rather than a round mark. If your approvals and your coding are done by different people at different times, two smaller stamps beat one crowded one.
The layout that survives an audit
A stamped invoice has to be legible after it has been scanned, filed and pulled back out three years later. That rules out a few things:
- Boxes, not free text. A labelled box tells the next person what is missing. A blank space does not.
- Room to write. A box under 8mm tall cannot hold a handwritten code. This is the single most common fault: the stamp is designed to look neat rather than to be written in.
- One colour, dark enough to scan. Blue is conventional for office use because on a photocopy you can see at a glance which is the original. Black photocopies best. Red is for exceptions like VOID.
- Position it clear of the invoice's own print. Top right is the convention because supplier layouts almost always leave it empty.
- A received date that fills itself in. Typing the date into the design fixes it forever; a date that resolves on the day of use records the day the invoice actually arrived.
Rectangular, and roughly this size
A coding stamp is a rectangle. About 60 by 40mm holds five or six labelled rows with writable boxes; the common 56 by 22mm office size holds two or three lines and no more. Anything you can fit into a circle is not a coding stamp, it is a RECEIVED mark.
What size a stamp should be covers the measurements in more detail.
Doing it on a file instead of on paper
Increasingly the invoice never gets printed, which is where a rubber block stops helping. The same grid works as an image applied to a PDF, and the PDF stamping tool processes the file in the browser rather than uploading it, which matters when the document carries a supplier's bank details.
For the number that has to advance on every document, the invoice serial stamp maker steps the counter itself rather than leaving somebody to remember the last one. For the simple case, stamp an invoice as paid.
Common questions about invoice stamps
What is an invoice coding stamp?
A rectangular block pressed on a supplier invoice that carries the fields a finance team fills in by hand: date received, GL or account code, cost centre, PO number, approver's initials and date paid. It puts the invoice's processing history on the invoice itself instead of in a separate system.
What should an invoice approval stamp include?
Received date, account code, approver and approval date at minimum, plus a PO field if the business uses purchase orders. Use labelled boxes rather than blank space, and make every box tall enough to write in, which in practice means at least 8mm.
What size is an invoice stamp?
About 60 by 40mm for a full coding grid with five or six writable rows. The smaller 56 by 22mm office size only holds two or three lines, so it works as a RECEIVED or PAID mark but not as a coding block.
Can I use an invoice stamp on a PDF?
Yes, and for invoices that arrive by email it is the only version that helps. Apply it as a transparent image in your PDF editor, or use a browser-based tool so the file with the supplier's bank details on it is not uploaded anywhere.
What colour should an approval stamp be?
Blue by convention for office use, because on a black and white copy you can tell the original from the copy at a glance. Black scans and photocopies best. Keep red for exceptions such as VOID or CANCELLED so it keeps its meaning.
The honest limits
Estamplab is a design tool, and this page describes common commercial and bookkeeping practice rather than giving legal, tax or accounting advice. What your own records must show, and how long you must keep them, is set by your tax authority and your auditor, so check the requirement with them or with your accountant.
Only produce a mark you or your organisation are entitled to use. Applying another business's mark to a document is forgery.
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