How to Write an Invoice: Complete Guide
A practical walkthrough of what belongs on an invoice, how to number them, and how to get paid faster — with a free generator at the end.
What Is an Invoice?
An invoice is a formal request for payment that a seller sends to a buyer after delivering goods or services. It's a legal record of the transaction — what was provided, how much it cost, and when payment is due — and it's what most small businesses use for bookkeeping, taxes, and resolving payment disputes.
What Should Every Invoice Include?
A complete, professional invoice should have:
- Your business details — name, address, email, and phone number
- Your client's details — the name and address you're billing
- A unique invoice number — for tracking and reference (see numbering tips below)
- The invoice date and, if applicable, a due date
- An itemized list of goods or services provided, with quantity, rate, and line total for each
- Subtotal, tax, discount, and total — shown separately so the math is easy to verify
- Payment terms — when payment is due and any late-payment policy
- Notes — payment instructions, a thank-you note, or any special terms
Invoice Numbering Best Practices
Invoice numbers exist so you (and your client, and your accountant) can find a specific invoice instantly. A few rules keep this simple:
- Make every number unique — never reuse one, even for a cancelled invoice
- Keep them sequential (e.g.,
INV-0001,INV-0002) so gaps are easy to spot - Pick a consistent format and stick with it — a prefix plus a zero-padded number works well
- Don't rely on dates alone as your only identifier — two invoices can share a date
Common Payment Terms, Explained
| Term | Meaning |
|---|---|
| Due on Receipt | Payment is expected as soon as the client receives the invoice. |
| Net 15 | Payment is due within 15 days of the invoice date. |
| Net 30 | Payment is due within 30 days — the most common term for B2B invoices. |
| Net 60 | Payment is due within 60 days, typically used with larger clients or longer sales cycles. |
| 2/10 Net 30 | A 2% discount if paid within 10 days, otherwise full payment is due in 30. |
Tips to Get Paid Faster
- Send the invoice immediately after finishing the work — don't let it sit
- State the due date explicitly rather than relying on payment terms alone
- Itemize clearly so there's nothing for the client to question or delay over
- Make it easy to pay by listing exactly how you accept payment
- Follow up before the due date, not just after it's overdue
- Keep a record of what's paid, pending, and overdue so nothing slips through
Do You Need Special Software?
Not necessarily — but a plain text editor or spreadsheet makes it easy to forget a field, miscalculate a total, or send something that looks unprofessional. A dedicated invoice generator handles the layout, math, and numbering for you, so every invoice looks consistent and nothing gets left out.
No sign-up required. Download as PDF or email it directly to your client.