Business document
Sales Invoice
The formal demand for payment. It is a legal document in most jurisdictions and a database record in your customer's — and the second of those decides whether it gets paid on time.
Also called: Bill · Tax invoice · VAT invoice · Commercial invoice (for export)
- Who sends it
- The supplier's finance or billing function, triggered by the despatch record rather than by the order.
- Who receives it
- The customer's accounts payable function — often a shared service centre in a different country from the buyer and the delivery site.
- When it is used
- On despatch, for goods sold on delivery terms. Earlier only where the contract provides for advance or milestone billing.
- Does it bind anyone
- Substantial and jurisdiction-specific. In most tax systems it is the document that evidences the supply, fixes the tax point and supports the customer's input tax recovery, with prescribed mandatory content. It is also the document a debt claim is built on. This is general description, not tax or legal advice — the specific requirements where you trade should be confirmed with your accountant.
What it is
An invoice is a supplier's demand for payment for goods or services supplied. It records what was sold, to whom, on what date, for how much, with what tax, and by when payment is due.
It has two audiences that want different things. Tax authorities require specific content, in a specific form, and treat omissions as defects. The customer's accounts payable system requires a set of reference numbers that let it match the invoice automatically against an approved purchase order and a posted goods receipt.
Those two audiences do not overlap much. An invoice can satisfy every legal requirement in the jurisdiction and still be unpayable because the customer's purchase order number is missing — and that failure is silent. Nobody at the customer is obliged to tell you.
Every field explained — 24 in total
What each field means, a realistic example value, whether you can leave it out, and the thing that goes wrong with it in practice.
| Field | What it means | Example | Needed? |
|---|---|---|---|
| The word 'Invoice' | Explicit identification of the document type.Watch out Sounds trivial; is a formal requirement in several jurisdictions. A document headed 'Statement' or 'Payment request' may not qualify as a tax invoice at all. | INVOICE | Required |
| Invoice number | A unique, sequential identifier.Watch out Must be sequential with no gaps and no reuse. This is why an issued invoice is never amended — you credit it and reissue with a new number, leaving both documents in the sequence. | INV-2026-04417 | Required |
| Invoice date | The date of issue. Payment terms usually run from here.Watch out Every day between despatch and invoice date is free credit given away. On a business turning over £20m, a three-day billing lag ties up roughly £164,000 permanently. | 17 April 2026 | Required |
| Tax point / supply date | The date the supply took place, which drives the tax period it falls in.Watch out Can differ from the invoice date, particularly across a period end. Getting it wrong puts tax in the wrong return. | Supply date 17 April 2026 | Conditional |
| Supplier name, address and legal identity | Who is demanding payment, as a legal entity. | Rochdale Precision Ltd, Unit 12 Sandbrook Way, Rochdale OL11 1RY. Registered in England 04482117. | Required |
| Supplier tax registration number | Your VAT, GST or sales tax registration.Watch out Its absence can prevent the customer recovering input tax, which turns a payment query into a formal rejection. | VAT GB 771 4482 09 | Required |
| Customer name and billing address | The legal entity being invoiced and where the invoice goes.Watch out The billing entity is frequently not the entity you have been dealing with, and frequently not in the same country as the delivery. Getting it wrong means an invoice that cannot be posted at all. | Northgate Engineering (Holdings) Ltd, Shared Services, Kraków, Poland | Required |
| Customer tax registration number | Their VAT or GST number, needed for cross-border and reverse-charge treatment. | VAT PL 5252445719 | Conditional |
| Customer's purchase order number | The order this invoice bills against.Watch out Commercially the most important field on the document. It is the join key their accounts payable system matches on, and an invoice carrying a number that does not exist in their system lands in an exceptions queue that nobody is assigned to clear. | PO 4500-887-2261 | Required |
| Purchase order line reference | Which order line each invoice line relates to.Watch out Required by systems that match at line level — which is most large ERPs. | PO line 010 | Conditional |
| Delivery note number and date | The despatch this invoice bills.Watch out This is what connects the demand for payment to a delivery the customer has already receipted. It is also the first thing you will be asked for when the invoice is queried. | DN-58117, 17 April 2026 | Required |
| Description of goods or services | What was supplied, in terms the customer recognises.Watch out Use the customer's part numbers. Their accounts payable clerk has never heard of your internal codes and cannot match on them. | NG-44821 Mounting bracket LH, drawing rev D | Required |
| Quantity | How many are being billed.Watch out Must equal the quantity despatched, not the quantity ordered. A mismatch against their goods receipt fails the three-way match and stops the invoice dead — this is the most common single cause of late payment on otherwise correct invoices. | 388 | Required |
| Unit price and line total | The agreed price and the extended value.Watch out Must match the price on the purchase order, including any agreed concession. Invoicing list price when a discount was agreed produces a short payment, and reconciling one costs more than the discount did. | £17.20 each, £6,673.60 | Required |
| Discounts and surcharges shown separately | Any adjustment applied, as its own line.Watch out Netting a discount into the unit price makes the invoice disagree with the purchase order price and fails matching, even though the total is right. | Volume discount 3% (−£200.21) | Conditional |
| Net total (before tax) | The taxable amount. | £6,673.60 | Required |
| Tax rate, amount and treatment | The rate applied, the amount charged, and the basis where it is not standard.Watch out Zero-rating, exemption and reverse charge each require specific wording on the face of the invoice. Getting it wrong can mean the invoice is rejected outright and reissued, restarting the payment clock from the new date. | VAT @ 20% — £1,334.72 | Required |
| Gross total payable | The amount due. | £8,008.32 | Required |
| Currency | The currency of the invoice, and the exchange rate where required for tax. | GBP | Required |
| Payment terms and due date | When payment is due, stated as an actual date rather than only as terms.Watch out Always print the calculated due date. 'End of month' terms are interpreted differently by different systems, and an explicit date removes an entire category of argument. | 60 days from end of month — due 30 June 2026 | Required |
| Bank details and payment methods | How to pay you.Watch out A prime target for invoice fraud. Never change bank details on an invoice without a separately verified notification to the customer — and expect them to phone a known number to confirm it, because they should. | Sort code 20-14-77, account 40028811, IBAN GB29 BARC 2014 7740 0288 11 | Required |
| Late payment terms | Interest or charges applicable if payment is late.Watch out Rarely enforced, but its presence is useful leverage in a collections escalation. | Interest chargeable on overdue amounts per our Conditions of Sale rev 4 | Optional |
| Retention of title statement | Ownership remains with you until payment. | Goods remain our property until paid in full. | Conditional |
| Remittance instructions | Where to send the remittance advice, and to quote the invoice number.Watch out One line, and it materially reduces the amount of unallocated cash you will have to investigate later. | Please email remittance to [email protected] quoting invoice number | Optional |
A filled-in example
Realistic values throughout — the sort of document that would actually pass through a business.
Invoice INV-2026-04417
- Invoice number
- INV-2026-04417
- Invoice date
- 17 April 2026
- Customer PO
- 4500-887-2261
- Delivery note
- DN-58117, 17 April 2026
- Bill to
- Northgate Engineering (Holdings) Ltd, Shared Services, Kraków
- Payment terms
- 60 days from end of month
- Due date
- 30 June 2026
| PO line | Description | Qty | Unit price | Net |
|---|---|---|---|---|
| 010 | NG-44821 Mounting bracket LH, rev D | 388 | £17.20 | £6,673.60 |
| 020 | NG-44822 Mounting bracket RH, rev D | 400 | £17.20 | £6,880.00 |
| 030 | NG-44830 Spacer, stainless 316, rev A | 1,600 | £2.45 | £3,920.00 |
- Net total
- £17,473.60
- VAT @ 20%
- £3,494.72
- Total payable
- £20,968.32
- Note
- Balance of 12 on PO line 010 to be invoiced on delivery.
- Payment
- Sort code 20-14-77, account 40028811 — quote INV-2026-04417
What happens next
- 01The invoice is sent by the route the customer requires — portal, EDI, e-invoicing network or a named accounts payable inbox.
- 02Their system matches it against the purchase order and the goods receipt. If all three agree, it is approved without human involvement.
- 03If they do not agree, it drops into an exceptions queue — usually with no notification to the supplier.
- 04The supplier's credit control confirms receipt and approval before the due date, rather than waiting for it to become overdue.
- 05On the due date, payment is made and allocated against the invoice, closing the transaction.
- 06If anything was wrong, a credit note is raised against this invoice number and a corrected invoice is issued.
Where it appears in the chain
- Raising the invoiceConverting a completed delivery into a demand for payment that the customer's systems can match and approve without a human having to intervene.
- Accounts receivable and collectionManaging what customers owe from the moment the invoice is issued until the money arrives — chasing before it is due, resolving queries fast, and escalating in a defined order.
- Payment and cash applicationThe money arrives — and then has to be matched to the right invoices, on the right accounts, so the ledger reflects reality and nobody chases a customer who has already paid.
Common mistakes
MistakeMissing or wrong purchase order number
Why it happens: Mistyped at order entry, or the customer issued a replacement PO nobody carried through.
What to do instead: Make it mandatory, print it on the acknowledgement so the customer can correct it early, and verify it against the current order before issue.
MistakeInvoicing the ordered quantity rather than the delivered quantity
Why it happens: The invoice is generated from the sales order rather than the despatch record.
What to do instead: Invoice from despatch, always. If the goods have not physically gone, they cannot be on an invoice.
MistakeAmending an issued invoice
Why it happens: The customer has not paid it yet and correcting seems simpler than crediting.
What to do instead: Credit in full, reissue with a new number. Two documents with the same number break the sequence, the tax record and both parties' audit trails.
MistakeSending it to the buyer
Why it happens: That is the contact everyone knows. In a large organisation they have no role in payment.
What to do instead: Hold the invoicing route as customer master data, established at account opening and re-confirmed after any reorganisation on their side.
MistakeBatching invoices weekly
Why it happens: It is administratively tidy and finance is busy.
What to do instead: Invoice daily or automatically on despatch. It is the only cash improvement available that requires no negotiation with anyone.
MistakeChanging bank details on the invoice without separate notification
Why it happens: The details are updated in the template as part of a bank change and nobody thinks further.
What to do instead: Notify separately and expect verification. Fraudulent invoices with altered bank details are one of the most common and most successful attacks on business payments — and a legitimate change that looks like one will be blocked anyway.
Terminology
- Three-way match
- The automated check that purchase order, goods receipt and invoice agree before payment is released.
- Tax point
- The date a supply is treated as taking place for tax purposes, determining which return it falls into.
- Reverse charge
- A mechanism where the customer rather than the supplier accounts for the tax, common on cross-border supplies. Requires specific wording on the invoice.
- Proforma invoice
- A document that looks like an invoice but is not one — used for advance payment requests or customs. It creates no tax point and no receivable.
- Self-billing
- An arrangement where the customer raises the invoice on the supplier's behalf from their own goods receipt.
- E-invoicing
- Structured electronic invoice submission, increasingly mandated by tax authorities and by large buyers' portals.
- Aged debt
- Outstanding invoices grouped by how overdue they are.
Common questions
›What must legally appear on an invoice?
The requirements are jurisdictional but typically include the word 'invoice', a unique sequential number, the date, both parties' identities, your tax registration number, a description of the supply, the net amount, the tax rate and amount, and the total. Confirm the specifics for where you trade — the general shape is consistent, the detail is not.
›Why do correct invoices go unpaid?
Because legal correctness and system matchability are different things. The usual causes are a purchase order number that does not match, a quantity that disagrees with the goods receipt, a price that differs from the approved order, or delivery to an entity other than the one billed. In each case the invoice sits in an exceptions queue and no one is obliged to tell you.
›Can you change an invoice after issuing it?
No. Raise a credit note referencing it and issue a corrected invoice with a new number. This is one of the few genuinely hard rules in the chain, because invoice numbering has to be sequential and unbroken for tax purposes.
›What is the difference between an invoice and a proforma invoice?
A proforma is a quotation formatted like an invoice — commonly used to request payment in advance or to support a customs declaration. It creates no tax point, no receivable and no obligation to pay. A real invoice must follow once the supply is made.
›When should the invoice be raised?
On despatch, from the despatch record. Earlier only where the contract provides for advance or milestone billing. Later is simply lost cash, because payment terms do not begin until the invoice is issued.
›How much does invoicing late actually cost?
Annual revenue ÷ 365 × days of delay is the cash permanently tied up. A £20m business invoicing three days after despatch has around £164,000 sitting in that gap every day of the year — and unlike renegotiating payment terms, closing it needs no conversation with any customer.
Tools for this
Downloadable, self-contained, and yours to keep — they run in a browser with no account and no data leaving your machine.
- Invoice GeneratorFreeCreate professional invoices for any country: 40+ currencies, VAT / GST / HST / sales-tax handling, tax-inclusive or tax-exclusive pricing, per-line discounts, and a built-in invoice register with paid / outstanding charts. Runs entirely in your browser. No installation, no account, no upload.
- Accounts Receivable AgingFreeAge your unpaid invoices into buckets, see what is overdue and by how far, work out days sales outstanding, and print a chase list for whoever is collecting. Runs in your browser. Nothing is uploaded.
Reviewed 2026-08-15. Nothing here is legal, tax or accounting advice — the mandatory content of commercial and tax documents varies by jurisdiction, so confirm the specifics for where you trade.