What is an invoice? What to include on one

An invoice is a document a seller sends to a buyer that lists what was supplied, what it costs and how much is owed. It asks for payment, and it is also a record: tax authorities use invoices as evidence of what you sold and the tax you charged or paid.

What it must show depends on your country and whether you are registered for VAT, GST or sales tax. Below are the rules for the UK, India and the US, checked against official sources on 2 October 2026. This is general information, not tax advice.

What every invoice should show

In any country, a clear invoice has:

• a heading such as "Invoice" or "Tax invoice"
• a unique invoice number
• the invoice date, and the date you supplied the goods or work
• your name or business name, address and contact details
• your customer's name and address
• a description of each item, with quantity and price
• the subtotal, any tax and the total due
• when payment is due and how to pay (for example, bank details)

In the UK and India, most of these are legal requirements.

UK: what an invoice must include

GOV.UK lists what every invoice must include: a unique identification number, your company name, address and contact details, the customer's company name and address, a clear description of what you are charging for, the supply date, the invoice date, the amounts charged, VAT if applicable and the total owed.

• Sole traders must also show their own name and any business name, and an address where legal documents can be delivered if they trade under a business name.
• Limited companies must show the full company name as it appears on the certificate of incorporation. If you list any directors, you must list all of them.

VAT invoices

If you and your customer are both VAT registered, you must issue a VAT invoice. HMRC's VAT Notice 700/21 (section 4.1) says it must show:

• a sequential number, in one or more series, that uniquely identifies the invoice
• the time of supply, and the date of issue if different
• your name, address and VAT registration number
• the customer's name and address
• a description of the goods or services
• for each item: the quantity, the unit price, the VAT rate and the amount excluding VAT
• the total excluding VAT, the rate of any cash discount, and the total VAT in sterling

You normally have to issue it within 30 days of the supply. For sales of £250 or less including VAT, a simplified invoice with fewer details is allowed (sections 4.4 and 4.5).

India: what a GST tax invoice must include

Under rule 46 of the CGST Rules, a registered person's tax invoice must contain, among other things:

• your name, address and GSTIN
• an invoice number (see numbering below) and the date of issue
• the customer's name, address and GSTIN if they are registered
• for an unregistered customer, their name, delivery address and state name and code when the taxable value is ₹50,000 or more (or when they ask)
• the HSN code for goods or SAC for services
• a description, and the quantity and unit for goods
• the total value, and the taxable value after any discount
• the tax rate and amount for central tax, State tax, integrated tax, Union territory tax or cess
• the place of supply with the State name for inter-State supplies, and the delivery address if it differs
• whether tax is payable on reverse charge
• a signature or digital signature (not needed on an electronic invoice issued under the IT Act)

Other rules that matter:

• Timing: for services, issue the invoice within 30 days of the supply (rule 47). For goods, issue it before or when the goods are removed or delivered (section 31).
• Bill of supply: if you supply only exempt goods or services, or you are in the composition scheme, you issue a bill of supply instead of a tax invoice (section 31(3)(c) and rule 49).
• E-invoicing: notified businesses must upload invoice details to the government portal to get an Invoice Reference Number (IRN) before issuing the invoice, and print a QR code that contains it (rule 48(4) and rule 46). An invoice that should have been made this way isn't treated as an invoice. Since 1 August 2023 this applies above ₹5 crore aggregate turnover (Notification 10/2023–Central Tax); check for later changes.
• Why buyers care: your customer generally needs your tax invoice to claim input tax credit (section 16(2)(a)).

US: no federal format

The US has no federal VAT or GST, and no federal rule on what an invoice must look like. The IRS says you can use any recordkeeping system that clearly shows your income and expenses, and it lists invoices among the documents that support your gross receipts. Keep a copy of every invoice.

Sales tax is set by states, and some have invoice rules. Washington, for example, requires sellers to state sales tax separately on invoices, and assumes tax wasn't paid if it isn't itemised. If you collect sales tax, check your state's department of revenue.

For a US invoice, follow the list at the top, with payment terms such as "due in 30 days" and any sales tax on its own line.

How to number invoices

• UK (VAT): use a sequential number, in one or more series, that uniquely identifies each invoice.
• India (GST): use a consecutive serial number of up to 16 characters, made of letters, numbers, hyphens (-) and slashes (/), unique for the financial year. You can run more than one series, for example one per branch.
• Everywhere: never reuse a number. A format with the year, such as INV-2026-0001, makes each number unique and easy to find. In India, a format like 2026-27/0001 resets cleanly each financial year and stays within 16 characters.

If you made a mistake on an invoice you've already sent, don't delete it or reuse its number. Issue a credit note or a corrected invoice, following your tax authority's rules.

Proforma invoice vs tax invoice

HMRC describes a pro-forma invoice as a document that sets out what will be supplied if payment is made. It says a pro-forma should be clearly labelled as one and preferably marked "This is not a VAT invoice" (VATREC9010). A buyer can't use it to reclaim VAT, and once you've been paid or made the supply you must issue a full VAT invoice within 30 days (VATREC9020).

In India, GST law doesn't define a proforma invoice. If you receive an advance payment, the law asks for a receipt voucher (section 31(3)(d)), and the tax invoice follows when you supply.

Make an invoice

Word, Google Docs and most spreadsheet apps have free invoice templates, and accounting software can number invoices for you. If you just need a quick, correct PDF:

• Invoice generator: any currency, your logo, tax, discounts and payment details. It also makes proforma and commercial invoices and quotes. No sign-up or watermark.
• GST invoice generator: an Indian tax invoice with the CGST and SGST or IGST split, GSTIN check, HSN/SAC and the amount in words. It doesn't generate an IRN, so if e-invoicing applies to you, use it only as a draft.
• GST calculator: add GST to a price or take it out of an inclusive amount before you invoice.

Both invoice tools make the PDF in your browser, without uploading it.