Invoicing Guide

What belongs on an invoice, how it differs from a proforma or a quote, invoice numbering, VAT inclusive versus exclusive, why totals come out a cent short, foreign currency, amounts in words, and payment terms.

• What to put on an invoiceThe fields an invoice needs, what each one is actually for, and the four the app refuses to let you skip.
• Invoice, proforma, quote or receiptThe four documents look alike and mean completely different things. What each one commits you to, and when to send which.
• How to number invoicesHow to number invoices so the sequence holds up: prefixes, zero padding, yearly resets, and why a missing number is a question you do not want asked.
• Tax inclusive or exclusiveThe difference between prices that include tax and prices that do not, how to back tax out of a gross price, and per-line rates.
• The missing centWhere the missing cent comes from, why per-line and per-total rounding disagree, and how the app avoids floating point entirely.
• Invoicing in a foreign currencyWhich currency to invoice in, what to state on the document, exchange rates, and the currencies where two decimals are wrong.
• The amount in wordsWhy documents ask for the total spelled out, how the line is constructed, and the details that make it correct in each currency.
• Payment terms and due datesWhat net 30 means, how to set a due date that is unambiguous, and what to write about late payment so it is worth writing.

This guide explains invoicing practice, not the law of your country. What an invoice must contain, how long you must keep it and how VAT is applied are set by your national tax authority and vary considerably. We guarantee the arithmetic and the layout; confirm the legal requirements with your tax authority or your accountant before you rely on them.