What Should Be on an Invoice? 10 Fields That Make It Legally Valid

Why Invoice Fields Matter

An invoice is not just a payment request — it is a legal document. In most jurisdictions, tax authorities specify exactly what information a valid invoice must contain. A missing field can mean a client's finance team rejects the invoice for processing, an accountant cannot accept it as a business expense, or a GST/VAT input tax credit claim is denied.

The good news: the required fields are consistent across most countries and are straightforward to include. Here are the ten that every invoice should have.

The 10 Must-Have Invoice Fields

Field-by-Field Detail

1. The Word "Invoice"

This seems obvious, but many homemade templates omit it. Under HMRC rules in the UK and the EU VAT Directive, a VAT invoice must be clearly labelled. Without it, the document is legally ambiguous.

2. Unique Invoice Number

Invoice numbers must be sequential and non-repeating. They do not need to start at 1 — many businesses use year-based prefixes like INV-2025-001. What matters is that no two invoices share a number, and that the sequence has no unexplained gaps (which can trigger audit questions).

3 and 4. Invoice Date and Due Date

The invoice date is the date of supply (or the date the invoice is issued, whichever comes first under GST rules). The due date is calculated from this: "Net 30" means 30 days after the invoice date. Both dates are essential for chasing overdue payments and for tax period calculations.

5 and 6. Seller and Buyer Details

For GST-registered businesses in India, both the supplier's GSTIN and the recipient's GSTIN (for B2B transactions) are mandatory under Section 31 of the CGST Act. For VAT-registered businesses in the UK and EU, the VAT registration number must appear on all VAT invoices. Even for non-registered businesses, a full address on both sides prevents disputes about which entity is party to the transaction.

7. Line Items

Vague descriptions invite disputes. "Consulting services — ₹50,000" is weaker than "Brand strategy workshop, 3 sessions × ₹16,667." Under GST, each line item may also need an HSN code (goods) or SAC code (services) to determine the applicable tax rate.

8. Subtotal, Taxes, and Total

Under India's GST system, CGST and SGST (for intra-state supply) or IGST (for inter-state supply) must each be shown as separate line items at the correct rate. Combining them or showing only a total tax figure is not compliant. The final total must be arithmetically consistent with the line items — an error here is grounds for rejection.

9. Payment Terms and Method

Stating payment terms reduces late payments. Research consistently shows that invoices with explicit due dates are paid faster than those that say only "payment due on receipt." Include bank account details, UPI ID, or a payment link to remove friction from the payment process.

10. Notes or Authorisation

A notes field serves multiple purposes: a thank-you message builds client relationships, a delivery note reference creates a paper trail, and an authorised signatory line (with name and designation) is required for formal procurement in many large organisations.

Use a Free Tool That Includes All 10

GoWin's free Invoice Generator includes fields for all ten of these elements. You do not need to remember the checklist — the tool's structure guides you through each one. The output is a clean PDF that meets requirements in India, the UK, the EU, and the US. No login, no subscription, no invoice limits.