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Invoices and collection · 6 min read

How to issue a correct tax invoice

What has to appear on a tax invoice, why an incomplete one gets refused, and how to correct one after it has gone out.

The short answer

A correct tax invoice carries the seller’s and buyer’s details, a sequential number that never repeats, a date, a description of each line with its quantity and price, the tax rate and amount, and the totals before and after tax. An invoice missing any of these may not be accepted for the buyer to deduct input tax — and that is the real damage: the buyer pays tax they cannot reclaim, then comes back asking you to reissue it.

The steps

  1. Start from a number that cannot repeat

    Each invoice gets one sequential number, never reused and with no unexplained gaps. The sequence is what lets a reviewer be sure they have seen every invoice and that none was quietly removed from the middle. Set the sequence once and leave it to the system; hand numbering produces two identical numbers in the first busy month.

  2. Name both parties in full

    The business name as it appears on its registration, its address, and its tax number if it is registered. If the buyer is a registered business, their tax number goes on too — without it their company cannot deduct the tax. A tax invoice with no seller tax number tells its reader the seller is not registered, which means they should not have been charging tax at all.

  3. Itemise the lines; never collapse them into one

    Every line with its description, quantity, unit price and amount. A single line reading "services" against a large figure makes the invoice unreviewable and leaves any later disagreement with the customer without a reference. The detail serves you first: when the customer returns one item, you know exactly how much to credit.

  4. Work out the tax per line, not on the total

    Lines can carry different rates: some standard-rated, some exempt or zero-rated depending on your country’s rules. Working tax out on the total gives a wrong figure the moment two lines differ, and produces rounding differences that surface at month end. Calculate per line, then add up.

  5. Write the total out in words

    The amount written out in words beside the figure is long-standing practice in Arabic business documents, and it is a simple, effective protection: a digit in a number can be altered, a written sentence cannot. Many customers and banks expect it, and its absence makes an invoice look unfinished even when it is correct.

  6. Correct with a credit note, never by editing

    An invoice that has been issued and handed over is never edited. A mistake is corrected with a credit note that names it by number, so the original stands as issued and the correction appears beside it. Software that lets you edit an issued invoice is software that lets you rewrite history, and that is what makes books untrustworthy.

Common mistakes

  • Issuing a tax invoice before being registered for tax. Charging tax without registration is a breach under most systems, and the customer accepting it does not make it right.
  • Reusing the number of a cancelled invoice. A cancelled invoice keeps its number and stays cancelled; the number is never given to another one.
  • Writing "tax included" without stating the amount. The buyer needs the figure itself to deduct, not just the rate.

Common questions

What is the difference between a tax invoice and a simplified one?
A tax invoice is issued to a registered business and carries its full details and tax number; a simplified one is usually for a final consumer and carries less. Which applies, and the threshold between them, is set by your own country’s rules.
Can an invoice be issued in a foreign currency?
In most systems yes, but the tax usually has to be shown in the local currency too, at the official rate on the date of supply. The books stay in the organisation’s own currency whatever the document is written in.
How long must invoices be kept?
The period differs by country and is commonly between five and ten years. Check your own rules, and keep the electronic copy in a format that will still open at the end of that period.

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