What should an invoice include?
An invoice should include the word “Invoice”, a unique invoice number, the invoice and due dates, full details for both you and your customer, an itemised list of what is being charged, the subtotal, any tax and discount, the total due, and how to pay. If you are tax-registered, it also needs your registration number and a tax breakdown by rate.
The required fields
These are the fields that appear on essentially every valid invoice, regardless of country or industry. Omitting one is the most common reason an invoice is queried or returned.
| Field | Required? | Notes |
|---|---|---|
| The word “Invoice” | Yes | Distinguishes it from a quote, estimate or receipt |
| Invoice number | Yes | Unique and sequential, no gaps |
| Invoice date | Yes | The date of issue; payment terms run from here |
| Due date | Strongly recommended | A specific date, not “on receipt” |
| Your business details | Yes | Legal/trading name, address, email |
| Your tax number | If registered | VAT/GST number — required for a tax invoice |
| Customer details | Yes | The legal entity being billed, not your contact |
| Customer tax number | If applicable | Required on tax invoices in many jurisdictions |
| Line items | Yes | Description, quantity, unit price, line total |
| Subtotal | Yes | Before tax |
| Tax breakdown | If charging tax | Rate and amount, per rate |
| Total due | Yes | The single number to be paid |
| Payment details | Yes in practice | Removes the commonest excuse for delay |
Fields worth adding even though they are optional
- Purchase order number — often mandatory in practice at larger companies, even when not legally required.
- A project or engagement reference, so the charge maps to the customer's own cost tracking.
- Service period, for retainers and recurring work.
- Notes — a one-line thank you, or context for an unusual charge.
- Payment terms in words, alongside the due date.
- A QR code for payment, which measurably reduces friction on mobile.
What changes for a tax invoice
A tax invoice has to let the buyer account for or reclaim the tax, which means the tax cannot simply be folded into a total. You need the taxable value, the rate applied, and the tax amount shown separately — per rate, if you charge more than one. Under Indian GST you additionally need HSN or SAC codes per line, both parties' GSTINs, and CGST/SGST shown separately for intra-state supply or IGST for inter-state supply.
What not to put on an invoice
- Bank credentials beyond what is needed to receive a payment — never passwords or full card numbers.
- Internal cost breakdowns or margins.
- Vague catch-all lines such as “miscellaneous”, which invite queries.
- A different total to the one you quoted, without an explanatory line.
Frequently asked questions
Does an invoice have to include a due date?
It is not universally required by law, but omitting it is a practical mistake: without a stated due date you have no clear point at which payment is late, which weakens any follow-up.
Do I need my customer's tax number on the invoice?
For a tax invoice to a registered business, usually yes — many jurisdictions require the recipient's registration number for them to reclaim the tax. For consumers, no.