Resource
The Complete Invoice Guide
Everything you need to know about invoices: what they are, the different types, the fields every invoice must include, the best-practice habits that get you paid faster, the mistakes to avoid, and how international invoicing differs from domestic.
What is an invoice?
An invoice is a commercial document issued by a seller to a buyer that records a sale and requests payment. It lists what was sold, the quantities, the prices, any applicable taxes, the total amount owed and the terms under which payment should be made. Beyond being a payment request, an invoice is a legal record of a transaction, the basis for accounting entries on both sides, and the source document a tax authority will ask to see during an audit. Treat it as a contract-adjacent document, not a casual email.
Types of invoices
The default sales invoice requesting payment for goods or services. Used in the majority of business-to-business and business-to-consumer transactions.
A preliminary document sent before work is delivered, often to confirm an order or arrange advance payment. Not a final demand for payment and usually not recorded as a sale in your books.
An invoice that meets the legal requirements of a tax authority — typically showing the supplier's tax ID, the tax rate, the tax amount and the total inclusive of tax. Mandatory under GST and VAT regimes.
Used in international trade for customs declarations. It describes the goods, country of origin, harmonised system codes, incoterms and the value for duty assessment.
Issued to reverse all or part of a previous invoice — for refunds, returns or corrections. References the original invoice number so the books stay consistent.
The mirror image of a credit note: a buyer sends it to a supplier to request an adjustment, usually when the supplier under-billed or goods were short-shipped.
An invoice raised automatically on a fixed schedule for repeat services like subscriptions, retainers or rent. Saves time and reduces the risk of a missed billing cycle.
A re-issue or reminder of an unpaid invoice after the due date, sometimes with late-payment interest added. Should clearly reference the original invoice number.
Required fields on every invoice
- The word 'Invoice' clearly displayed
- Unique invoice number and issue date
- Supplier name, address and tax ID
- Customer name and billing address
- Description, quantity and unit price for each line
- Subtotal, tax, any discount and grand total
- Currency, payment terms and due date
- Accepted payment methods and account details
Some jurisdictions add requirements — for instance, India's GST rules mandate the supplier's and recipient's GSTIN, place of supply, and a split of CGST and SGST or IGST. EU VAT invoices above a threshold must show the supplier's and customer's VAT numbers. Check local rules before sending your first invoice.
Best practices
Send invoices the day you deliver the work — every day you wait is a day added to your cash cycle. Number invoices sequentially and never reuse a number. Keep a master list of every invoice you issue with its status (sent, paid, overdue). Use a consistent template so clients recognise your documents instantly. State the due date as a specific calendar date, not a vague phrase. Make payment frictionless by listing every method you accept and including account details or a payment QR code in the document itself.
Common mistakes to avoid
Without a unique sequential number, matching payments to invoices becomes guesswork. Pick a numbering scheme on day one and stick to it.
'Services rendered' invites disputes. Describe the work in enough detail that the client can approve it without coming back to you.
Charging the wrong rate, forgetting reverse charge, or omitting your tax ID can invalidate the invoice and trigger penalties.
A wrong subtotal or tax figure is the most common reason an invoice is bounced back. Use a live-preview generator that handles the arithmetic.
'Payment due on receipt' is open to interpretation. Use 'Net 14' or a specific date so there is no ambiguity.
If you cannot prove when an invoice was sent, chasing late payment becomes harder. Email it, log the date and keep the PDF.
Legal requirements
Most countries require invoices above a certain value to be retained for a defined period — typically five to ten years — and to contain specific fields, particularly when tax is involved. Electronically issued invoices often need to meet authenticity, integrity and readability requirements, which in practice means a clean PDF with all the mandatory fields. Some jurisdictions, including Italy and India, are moving toward real-time or pre-clearance e-invoicing where invoices must be reported to a government portal before or at the moment of issue. Always confirm the rules that apply to your country and your customer's country.
International invoicing
Cross-border invoices carry extra considerations. Currency choice matters: invoicing in your own currency shields you from exchange-rate movement but may put off foreign clients, while invoicing in theirs shifts the risk to you. State the currency clearly and consider a forward contract if the amount is large.
Tax treatment changes too. Exports are often zero-rated under GST or VAT, but you must still document the export correctly — including the place of supply and the customer's tax ID. The reverse-charge mechanism, where the customer accounts for tax instead of the supplier, is common in B2B services between EU member states and in many other regions.
For physical goods, customs requires a commercial invoice with harmonised system codes, country of origin, incoterms and declared value. Bank details should include IBAN and SWIFT/BIC codes, and you should warn the client about intermediary bank fees so the amount you receive matches the amount on the invoice.
Keep reading
Pair this guide with the step-by-step walkthrough and the tax-specific guides.