Last updated November 6, 2026
Rules and figures from other sources checked on November 6, 2026. They change, so confirm with the source before you rely on them.
General information, not tax or legal advice. The rules depend on your country and your situation, so check anything with a tax or legal consequence with your accountant.
To invoice a client, agree the price and payment terms, then issue a document with a unique number, both parties' details, the issue date, a description of the work, the amounts and any VAT, a due date and how to pay. Send it as a PDF to whoever pays the bills, then track it until paid.
An invoice does two jobs. It asks for money, and for a VAT-registered business it is also a tax record your customer may use to reclaim VAT. The tax job decides what must be on it. The collecting job is yours to get right, because VAT rules don't ask for a due date or bank details.
What must an invoice include?
An EU VAT invoice must include the details listed in Article 226 of the VAT Directive. Here they are in the order you'd fill them in, with the point number and the mistake each one attracts.
| Detail | Art. 226 point | The usual mistake |
|---|---|---|
| Issue date | (1) | Back-dating it to fit a period |
| Sequential number that uniquely identifies the invoice | (2) | Numbering by customer, or reusing a number. See how to number invoices |
| Your full name and address, and your VAT number | (3), (5) | A trading name with no legal name |
| Customer's full name and address | (5) | The contact's name instead of the company's |
| Customer's VAT number, where the customer accounts for the VAT or buys goods from another EU country | (4) | Left off a reverse-charge invoice |
| Quantity and nature of the goods, or extent and nature of the services | (6) | "Services rendered" |
| Date of supply, if different from the issue date | (7) | Left off when the work finished last month |
| Net amount per VAT rate, unit price before VAT, any discount | (8) | A discount buried inside a price |
| VAT rate and VAT amount | (9), (10) | One rate applied across mixed lines |
| Why no VAT is charged: the exemption reference, or the words "Reverse charge" | (11), (11a) | Zero VAT with no explanation |
That list is what VAT law asks for. The due date and your payment details aren't on it, and you need them anyway. An invoice without them can be perfectly valid and still not get paid.
The list changes in a few situations:
- In the UK, HMRC's VAT guide gives a very similar list at paragraph 16.3.1, and asks for the time of supply, known as the tax point.
- If you aren't VAT registered, you charge no VAT and don't issue a VAT invoice. GOV.UK's list for ordinary invoices still asks for a unique number, both parties' details, a clear description, the supply date, the invoice date and the amounts.
- For small amounts, EU countries must allow a simplified invoice up to €100 (Article 220a, with exceptions for some cross-border sales). The UK allows one up to £250 if the customer agrees (paragraph 16.6.1 of HMRC's guide).
- Your country may add more. Article 226 covers VAT only. Company or tax law can add details such as a registration number, so ask your accountant once and build the answer into your template.
Each field is explained in full in VAT invoice template fields.
How to invoice a client, step by step
- Agree the price and the terms first. Put the scope, the price and the payment term in a quote or an email the client has replied to. An invoice is a poor place for a client to learn what something costs.
- Collect the billing details before you need them. You want the legal name, the billing address, a VAT number if they have one, any purchase order number, and the address invoices should go to. The person who hired you often doesn't know these, so ask them to find out.
- Choose the billing moment. That may be on completion, on a deposit, at stages or monthly. The table further down helps.
- Write the lines so a stranger can approve them. Someone in accounts who has never met you will pass "Shopfront sign, 2.4 m, installed 10 April". "Signage" gets a query.
- Work out the tax on each line. Domestic sales normally take your local rate. For anything crossing a border, read how to invoice EU clients or how to invoice international clients first.
- Set the dates. The issue date is today. Make the due date an actual date, worked out from your payment terms, because "28 April 2026" leaves less to argue about than "net 14".
- Say how to pay. Give the account name, IBAN and BIC, and ask for the invoice number as the payment reference so you can match the money when it lands.
- Issue it, then leave it alone. This is when the number is assigned and the invoice becomes final. A mistake found later gets a credit note or a cancel and reissue, never a quiet edit.
- Send it to the right inbox. Email the PDF to the accounts address and copy your contact, with a short email that gives the number, amount and due date in the first lines. Check that a PDF is enough, because some countries now require structured e-invoices. Belgium has done so between VAT-liable businesses since 1 January 2026.
- Record the payment or chase it. Note the due date. If the money hasn't arrived the day after, start your reminder sequence.
A complete invoice, worked through
Here's an invented example: a sign maker billing a café for a new shopfront sign, with 20% VAT for illustration.
| Field | On this invoice |
|---|---|
| Invoice number | INV-2026-0042 |
| Issue date | 14 April 2026 |
| Date of supply | 10 April 2026 |
| Due date | 28 April 2026 |
| Customer's order number | PO 5518 |
| From | Harbour Signs Ltd, 4 Quay Street. VAT no. XX123456789 |
| To | Corner Café Ltd, 18 Mill Road. VAT no. XX987654321 |
| Payment | Bank transfer to Harbour Signs Ltd, IBAN XX00 0000 0000 0000. Reference INV-2026-0042 |
| Description | Qty | Unit price | VAT | Net |
|---|---|---|---|---|
| Sign design, hours | 6 | €65.00 | 20% | €390.00 |
| Aluminium shopfront sign, 2.4 m | 1 | €1,250.00 | 20% | €1,250.00 |
| Installation, 10 April | 1 | €280.00 | 20% | €280.00 |
| Net total | €1,920.00 | |||
| VAT at 20% | €384.00 | |||
| Total due | €2,304.00 |
Three choices on that invoice are deliberate. The date of supply appears because it differs from the issue date. If you invoice on the day you finish, one date does both jobs. The design work shows hours and a rate because HMRC treats an hourly rate as the unit price of a service (paragraph 16.3.2), while the sign is one item at its full price. And the customer's order number is on there because some accounts teams won't release payment without it.
When should you send an invoice?
You should send an invoice as soon as the agreed billing moment arrives, because payment terms usually count from the invoice date or from when the client receives it.
| How you work | When to invoice | Read next |
|---|---|---|
| One-off job | The day it's finished or delivered | |
| Bigger job with a deposit | On acceptance, then on completion | Deposit and final payment |
| Long project | At the stages you agreed up front | Progress billing |
| Regular service | The same date every month | Monthly retainer |
| Hourly work | Month end, or each agreed stage | Hours into an invoice |
VAT rules set the outer limit. In the UK you normally issue a VAT invoice within 30 days of the tax point (paragraph 16.2.3 of HMRC's guide). In the EU, cross-border services under the reverse charge must be invoiced by the 15th day of the following month (Article 222), and each country can set limits for other supplies.
What happens if an invoice has no agreed due date?
An invoice with no agreed payment date is treated as late 30 days after the client receives it, or 30 days after delivery if that came later, for business customers in the EU (Article 3 of the Late Payment Directive) and the UK (GOV.UK).
So if you want 14 days, agree 14 days before you start. Printing it on the invoice for the first time is weaker than having it in the quote the client accepted. Agreed terms between businesses can run to 60 days, and longer only if expressly agreed and fair.
Why do invoices get sent back?
Invoices usually get sent back because the accounts team can't match them to something already approved. These are the ones to check before you press send:
- The wrong legal entity. The contract is with a holding company and the invoice names the shop.
- No purchase order number, when the customer's system won't accept an invoice without one.
- A description nobody can approve. The person paying wasn't in the meeting.
- A total that differs from the quote, with no line explaining why.
- A missing or wrong VAT number, which can stop the customer reclaiming the VAT.
- The wrong inbox. Your contact is on leave, and the invoice is on leave with them.
Invoicing clients in ERPFlow
In ERPFlow, an invoice starts as a draft against a customer record. You add lines, picking a service or product to fill in the description and price, with an optional discount and a tax rate on each line. The due date starts at 14 days after the issue date, and you can change it. Your legal name, VAT number, address and bank details come from Settings > Business Info.
Issue gives the invoice its number, such as INV-2026-0042, and makes it final. Send via email delivers the PDF, in any of 19 languages, and records the delivery. After that, Record payment tracks full or part payments, the Overdue filter shows what's late, and Send payment reminder emails a reminder, one invoice at a time.
There are limits to know about. ERPFlow has no separate date-of-supply field, so when that date differs from the issue date, write it in the line description or Notes. There's no online card payment. It doesn't check VAT numbers in VIES or choose a rate from the customer's country. E-invoices export as Peppol BIS Billing 3.0 XML for you to pass to your e-invoice operator, and ERPFlow doesn't send them over the Peppol network itself.