How to write an invoice
An invoice needs five things: your details, your client’s, a number and a date, a breakdown of what you’re charging for, and the total. That’s enough for a client to accept it and pay it.
What does an invoice need to include?
Yours (name or business name, tax ID, address and a way to reach you), your client’s (at least a name and a tax ID), a number that doesn’t repeat, the issue date, each line item with its quantity and price, and the total.
If payment isn’t immediate, add a due date and how you want to be paid. That’s what speeds up payment more than anything: the client doesn’t have to ask.
How do you number an invoice?
With a sequence that doesn’t repeat or skip. The most practical is year plus a running number: 2026-0001, 2026-0002, and so on.
Numbering matters for two reasons: it lets you track what you’ve been paid for, and it gives the client a reference for their own books. A repeated number causes confusion and delays payment.
What’s the difference between an invoice and a quote?
A quote proposes: it says what a job would cost, and the client accepts it or doesn’t. An invoice charges: it’s issued once the work is done or agreed, and it asks for payment.
In practice the document looks much the same: same details, same line items, same totals. What changes is the timing and the intent. A quote usually carries a validity period ("valid for 30 days"); an invoice, a due date.
How is the total worked out?
You add up each line item (quantity × unit price) to get the subtotal. Any discount comes off that. Tax is applied to what’s left. The result is the total.
The order matters: tax is worked out after the discount, not before. If you add up 100,000, apply a 10% discount and 21% tax, the total is 108,900 — not 111,000.
Do I need a tax ID to invoice?
For an official invoice with legal standing, yes: every country has its own system and identifier. For a payment document between two parties — which is what this tool makes — it isn’t required, though including it builds trust.
This tool makes documents, not tax records. If your client needs an official invoice to claim the expense, you have to issue it through your country’s tax system.
What format should I send it in?
PDF. It looks the same on any device, it can’t be edited by accident, and it’s what accounts departments expect.
Avoid sending a Word file or a spreadsheet: they break when opened on another machine, and an editable file invites someone to change a number.
Make yours now
The generator builds the document as you type and works out the totals for you.