What to Include on an Invoice: The Eight Fields That Matter
The anatomy
Every invoice, in every country, is a variation on this layout:
┌───────────────────────────────────────────────────────────┐
│ INVOICE No. INV-2026-001 │ 1 what it is
│ Issued 12 March 2026 │ 2 unique number
│ Due 11 April 2026 │ 3 issue date
├───────────────────────────────────────────────────────────┤
│ FROM │ BILL TO │
│ Anna Petrova │ Northwind Ltd │ 4 who you are
│ Yerevan, Armenia │ 12 Market St, Dublin │ 5 who they are
│ Tax ID 01234567 │ VAT IE1234567X │
├───────────────────────────────────────────────────────────┤
│ Description Qty Rate Amount │
│ UX audit 1 1 200.00 1 200.00 │ 6 what you delivered
│ Design revisions 4 75.00 300.00 │
├───────────────────────────────────────────────────────────┤
│ Subtotal 1 500.00 │
│ VAT 20% 300.00 │
│ TOTAL DUE 1 800.00 EUR │ 7 the amount
├───────────────────────────────────────────────────────────┤
│ Payment │
│ Bank: Example Bank · IBAN AM00 0000 0000 0000 │ 8 how to pay
│ Reference: INV-2026-001 │
└───────────────────────────────────────────────────────────┘
The eight, and why each exists
1. The word "Invoice". Not decoration. It distinguishes the document from a quote, an estimate or a proforma — which look identical but create no obligation to pay. A client's accounting department sorts by this word.
2. A unique number. The one field with a hard rule behind it: unique, sequential, never reused. It is how your records are audited and how your client references the payment. Formats and pitfalls are in how to number invoices.
3. The issue date. Starts the payment clock and places the invoice in a tax period. If your due date is "net 30", it is thirty days from this date.
4. Who you are — in full. Legal name (not just a trading name), address, and tax identifier if you have one. "Anna, anna@example.com" is not enough for a company to pay against: their finance system needs a payee record.
5. Who the client is — in their full legal form. The single most common cause of a
rejected invoice. Northwind Ltd and Northwind Group Holdings BV may be the same people to
you and two different legal entities to their accounts payable. Ask which entity to bill;
do not infer it from the email signature.
6. What you delivered. One line per item, with quantity and rate where they apply. "Consulting — 3 000.00" gets queried. "UX audit, 1 × 1 200.00" does not. Write it so that somebody who was not in the meetings can approve it.
7. The total due. In a currency, stated explicitly. 1 800.00 is ambiguous;
1 800.00 EUR is not. If you charge tax, show the subtotal, the tax and the total
separately — the client's bookkeeping needs all three.
8. How to pay. Bank name, IBAN (or local account number), account holder name, SWIFT/BIC for cross-border. Add a payment reference — usually the invoice number — so the incoming transfer can be matched to the invoice without an email exchange.
Optional, but they earn their place
| Field | When it is worth adding |
|---|---|
| Due date | Always. "Payment terms: 30 days" is a policy; a date is an instruction |
| PO number | Whenever the client has one. Without it, larger companies cannot process the invoice at all |
| Payment terms | "Net 30", "50% on signature" — the agreement, in writing, on the document |
| Contact person | Who at the client approved the work. Speeds up the internal chase |
| Notes | Delivery details, project reference, validity of quoted rates |
| Your logo | Recognition, and it makes the invoice look like it came from a business |
Tax lines: the short version
If you are registered for VAT (or an equivalent), the invoice must show your tax number, the rate applied, the tax amount, and the totals before and after it.
For B2B sales across an EU border, the reverse-charge mechanism usually applies: you invoice without VAT, the buyer accounts for it in their own country, and the invoice carries both VAT numbers plus a note such as "Reverse charge — VAT to be accounted for by the recipient".
If you are not registered, you charge no tax and show no tax line. Do not invent one.
Cross-border extras
- Currency, named explicitly, on the total.
- SWIFT/BIC alongside the IBAN.
- The account holder's name exactly as the bank has it. Mismatches here bounce transfers more often than wrong digits do.
- Who pays the transfer fee — worth one line in Notes if the amount matters.
Four omissions that delay payment
- No due date. "Payment on receipt" means "whenever" to an accounts payable queue.
- No PO number where the client uses them. The invoice cannot enter their system.
- Wrong legal entity. Rejected, returned, reissued — two weeks gone.
- Bank details on a second page or in the email body. Put them on the invoice itself.
If an invoice is already late, the sequence to work through is in what to do when an invoice is overdue.
How this maps to the builder
The Kinvoice builder is laid out in this order on purpose — Document, From, Bill to, Items — so filling it top to bottom produces a complete invoice without a checklist. The walkthrough is in how to create an invoice online.
Two things carry over between invoices with a PRO account: the company profile (your details, tax number and bank accounts, filled once) and automatic numbering, so field 2 stops being something you have to remember.
Requirements differ between countries, and some impose additional mandatory fields — this describes common international practice, not tax advice. Confirm anything that affects your reporting with your accountant.
FAQ
What are the minimum fields on an invoice?
The word "Invoice", a unique number, the issue date, your details, the client's details, a description of what you delivered, the total due with its currency, and how to pay. Everything else is optional.
Do I need a company to issue an invoice?
In most countries an individual can invoice, though what you must show — a tax number, a registration status — depends on where you are and how much you earn. Check the rules for your own country before you rely on it.
Do I have to show VAT on an invoice?
Only if you are registered for it. If you are, show your tax number, the rate, the tax amount and the totals before and after. If you are not registered, charge nothing and show no tax line.
What is a PO number and do I need one?
A purchase order number is the reference a client's finance system raises before work starts. If your client uses them, an invoice without one usually cannot be processed at all — ask for it before you invoice.