What a correct invoice contains
Updated 30 October 2026 · 7 minute read
An invoice is a request for payment and a record of a sale. When it is complete, everyone involved — your customer, their accounts department and, if it comes to it, a tax officer — can see what was sold, for how much, and when it should be paid. When it is incomplete, payment slows down, disputes start, and bookkeeping becomes guesswork.
The good news is that a correct invoice is not complicated. The checklist below covers what a small business, freelancer or shop needs in almost every country.
The fields every invoice should have
| Field | Why it matters |
|---|---|
| Your business name and address | Identifies who is owed the money |
| Your contact details | Lets the customer ask a question before paying |
| The word “Invoice” | Distinguishes it from a quotation or a receipt |
| A unique invoice number | Makes the document traceable in both ledgers |
| Invoice date and due date | Starts the payment clock |
| Customer name and address | Shows who must pay |
| Description of each item or service | Proves what was delivered |
| Quantity and unit price | Lets the customer check the arithmetic |
| Subtotal, discount, tax, total | Shows how the final figure was reached |
| Payment instructions | Removes the most common cause of delay |
Many tax systems also require a tax registration number, and some require the customer’s tax number when the sale is business-to-business. Check the rules that apply where you are registered.
Numbering invoices so they never collide
A simple scheme that scales well is prefix-year-sequence, for example INV-2026-001, INV-2026-002, and so on. Reset the sequence each year and keep the previous year’s files together. Avoid reusing a number after a cancelled invoice: mark the cancelled one as “VOID” and keep it in the sequence so the audit trail stays intact.
If you issue separate series for different customers or branches, use a distinguishable prefix — SHOP2-2026-014 — rather than starting a second sequence in the same range.
Order of operations: discount and tax
The order matters, and the two common conventions are not the same number:
- Discount before tax. Subtotal → minus discount → tax on the reduced amount. This is the usual approach when a discount is a trade discount given at the point of sale.
- Tax before discount. Tax on the full subtotal → then discount applied to the total. This is used for some promotional schemes and is less common on standard invoices.
Our invoice generator uses the first convention, which is the easier one to explain to a customer: a 10% discount on PKR 57,000 gives PKR 51,300, and 5% tax is charged on PKR 51,300, not on PKR 57,000.
Payment terms that get you paid
“Payment due within 7 days” is clearer than “payment due soon”, and far clearer than nothing. Useful wording includes the deadline, the accepted methods, and what happens if the deadline passes:
Late fees are only enforceable if the customer agreed to them in advance, for example in a signed quotation or terms of service. Otherwise they are a nudge, not a legal right.
Common mistakes
- No invoice number. The customer’s accounts team cannot file it, so it waits.
- Vague descriptions. “Services — 45,000” invites a question; “Website design, 5 pages, delivery 20 Oct — 45,000” does not.
- Wrong date format. 03/04/2026 is March or April depending on the reader. Write “3 April 2026”.
- Missing currency. PKR 50,000 and USD 50,000 are very different invoices.
- Totals that do not add up. Check each line, then the subtotal, then the total.
- No copy kept. Save a PDF of every invoice you send.
How to produce a PDF
Fill in the generator, check the preview, then press Print / Save as PDF and choose “Save as PDF” in the print dialog. The result is a clean single-page document without browser headers if you switch off “headers and footers” in the dialog. Keep the PDF alongside your records — the site does not store anything for you.