What an invoice has to contain
Requirements vary by jurisdiction, but a common core applies almost everywhere: the word "invoice", a unique sequential number, the issue date, your name and address, the customer's name and address, a description of what was supplied, the amount due, and the payment terms.
Tax registration adds requirements. A VAT-registered business in the UK or EU must show its VAT number, the tax rate applied, the net amount, the tax amount and the gross total, and must issue a compliant VAT invoice for the customer to reclaim the tax. Cross-border supplies within the EU need the customer's VAT number and a note that the reverse charge applies. US requirements are generally lighter, with sales tax handled at state level and varying considerably.
Invoice numbers should be sequential and never reused. Gaps and duplicates are exactly what an audit looks for, and if an invoice must be cancelled, the correct procedure is a credit note referencing it rather than deleting or renumbering.
Terms that actually get you paid
Payment terms should be explicit and stated as a date rather than a period — "due 30 September 2026" is clearer and harder to dispute than "net 30", which raises the question of whether the clock starts at issue, at receipt or at month end. Shorter terms are worth asking for; 14 days is common for smaller suppliers and there is nothing improper about requesting it.
For larger projects, staged payment is the main protection against non-payment: a deposit before starting, a milestone payment partway, and the balance on completion. It caps exposure at one stage rather than the whole engagement, and a client unwilling to pay a deposit is information worth having early.
Late payment legislation exists in many jurisdictions and is under-used. In the UK, the Late Payment of Commercial Debts Act entitles a business to statutory interest plus a fixed compensation sum on overdue commercial invoices without needing it in the contract; the EU Late Payment Directive is comparable. Stating on the invoice that statutory interest will be charged makes it easier to apply later.
Practical habits
Invoice promptly. Payment terms start when the invoice is issued, so a week's delay in sending is a week's delay in being paid, and invoicing at the point of delivery — while the work is fresh in the client's mind — measurably reduces disputes.
Send to the right place. Larger organisations have accounts payable processes, purchase order requirements and specific portals, and an invoice sent to your day-to-day contact may sit unactioned for weeks. Asking who receives invoices and whether a purchase order number is required, before starting work, prevents the most common cause of slow payment.
Keep copies for as long as your jurisdiction requires — commonly six years in the UK and Ireland, and varying elsewhere. This generator produces a document from the information you enter, entirely in your browser, and does not constitute tax, accounting or legal advice. Requirements differ by country and by business type, so check with an accountant or your tax authority for what your invoices must show.