How to Write an Invoice: What to Include, What to Charge, and When to Send It

• Your business name and contact info. Legal or trade name, address, email, phone. If the client has a question about the bill, they need to know who to call.
• The client's name and billing info. Who's actually responsible for paying — a person or the company, matched to how you'll pursue payment if it's late.
• An invoice number. A unique identifier (sequential is simplest: INV-001, INV-002) so you and the client can both refer to “invoice 014” instead of “that thing from last month.” This is also what makes an invoice traceable as a financial record, not just a note.
• The invoice date. The day you're issuing it — this is what payment terms like “Net 30” count from.
• Payment terms and a due date, spelled out as a real calendar date. State the terms (“Net 30,” “Due on Receipt,” etc.) and the actual date — write “Net 30 — Due October 12, 2026,” not just “Net 30.” Nobody should have to do the math themselves, and a specific date is much easier to enforce than a term alone.
• An itemized description of the work or goods. What you did or sold, in enough detail that the client (and you, six months later) can tell what it was for. “Consulting services” is vague; “Website copywriting — homepage and 3 landing pages” is an invoice.
• Quantity, rate, subtotal, tax (if any), and total due. In the U.S. that's sales tax where it applies; in Canada it's GST/HST (and PST/QST in some provinces) if you're registered to charge it. Show the math, not just a final number — it's the difference between a bill someone trusts and one they call you to question.
• How to pay. Accepted payment methods, and where to send payment (bank details, payment link, mailing address). If you invoice clients in both currencies, note which currency the total is in — USD and CAD are not interchangeable on a bill.

• Under $100: your business name, the invoice date, and the total amount are enough.
• $100 to $499.99: add the GST/HST amount (or a note that it's included) and your GST/HST registration number.
• $500 or more: add the buyer's name, a description of what was sold, and your payment terms.

• Due on receipt — payment is expected as soon as the client gets the invoice. Common for one-off or first-time clients.
• Net 15 / Net 30 / Net 60 — payment is due that many calendar days after the invoice date, not the date the client opens the email. Net 30 from an invoice dated September 12 is due October 12 — weekends and holidays count unless you say otherwise.
• 2/10 Net 30 — a compound term meaning: pay within 10 days and take a 2% discount, otherwise the full amount is due in 30 days. It rewards early payment without penalizing the client for using the full window.

Write the actual due date, not just the term

“Net 30” alone makes the client do arithmetic — a real date removes the excuse for a late payment being “a misunderstanding.”

• No invoice number — makes it impossible to reference the bill precisely, and harder to prove it existed if a client claims they never got one.
• “Net 30” with no calendar date — gives every late payer a built-in excuse.
• Vague line items — “services rendered” invites a client to ask questions instead of just paying.
• Waiting to send it — the single biggest lever you control over how fast you get paid is how fast you invoice.
• Mixing up currency or tax rules — if you invoice across the border, double-check which tax applies (sales tax vs. GST/HST) and which currency the total is in before you hit send.

Sources

• IRS — What kind of records should I keep — supports invoices as a core supporting document for gross receipts and expenses.
• IRS — How long should I keep records? — U.S. record-retention periods (generally 3 years, with exceptions).
• Canada Revenue Agency — RC4022, General Information for GST/HST Registrants — exact input-tax-credit information thresholds required on invoices issued by GST/HST registrants.
• Canada Revenue Agency — GST/HST records to keep — the Canadian 6-year record-retention requirement.