Guide · 9 min read

How to write an invoice in Singapore: what it must show, with a template you can copy

An invoice template for Singapore needs fewer boxes than most people expect, but each one earns its place: who you are, who you're billing, a number that's never reused, the date, what you supplied, the amount, and when and how to pay. If you're GST-registered, IRAS adds its own list for a tax invoice, which must reach a GST-registered customer within 30 days of the supply.

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Below: both cases, numbering, payment terms, credit notes and a worked example to copy. Sources are listed at the end; GST rules change, so check IRAS before relying on a detail.

What every invoice should show

GST-registered or not, a clear invoice answers what a customer's accounts team asks before paying:

  • The word 'Invoice' at the top.
  • Your business name as registered with ACRA, your UEN, address and contact details.
  • A unique invoice number in sequence, such as INV-0042, and the date of issue.
  • The customer's name and, for a company, its full name, address and who it's for.
  • Each item on its own line: a clear description, quantity, unit price and line total.
  • The total, any deposit already paid, and the balance due.
  • A due date and how to pay: your PayNow UEN or mobile number, or bank account details.
  • The customer's PO number, if they gave one. Many companies won't pay without it.

If you're not GST-registered

Most new businesses aren't GST-registered: registration is compulsory only once taxable turnover passes S$1 million in a calendar year, or is expected to within the next 12 months. Until then, your invoice has no GST line. Don't add 9% or title it 'Tax Invoice'. IRAS doesn't allow unregistered businesses to charge GST, and asks anyone who collected it by mistake to come forward and pay it over.

If you're GST-registered: what a tax invoice must show

IRAS sets out what a tax invoice must contain, and all of it has to be on one document:

  • The words 'Tax Invoice', in a prominent place.
  • Your name, address and GST registration number.
  • An invoice identifying number and the date of issue.
  • The customer's name and address.
  • A description of the goods or services.
  • The GST rate, the total excluding GST, the GST amount and the total including GST. For a zero-rated supply, show GST at 0%.

Deadlines, receipts and simplified tax invoices

The 30-day deadline is for GST-registered customers; others don't need a tax invoice at all: IRAS accepts a serially numbered receipt showing your name, GST number, the date, the total including GST and a note that the price includes GST, with a duplicate kept. For a sale of S$1,000 or less including GST, a simplified tax invoice without the customer's details is allowed. Bills in another currency must show the amounts converted into Singapore dollars at IRAS's approved exchange rates for GST.

Numbering that holds up

A few rules keep the series clean:

  • One running sequence, never reused, even when an invoice is cancelled.
  • Never delete an issued invoice. Mark it cancelled or correct it with a credit note, so every gap has an explanation.
  • Keep credit notes in their own series, such as CN-0001.
  • Keep dates and customer names out of the number itself.
  • Keep copies: IRAS asks businesses to keep records such as invoices and receipts for five years.

Payment terms that get you paid on time

'Net 30' means little to a home owner. Spell it out:

  • Write a date: 'Please pay by 18 November 2026' gets paid sooner than '14 days'.
  • Households usually pay on completion or within 7 days; companies often expect 14 or 30 days.
  • Ask customers to quote the invoice number with their payment, so each transfer matches a bill.
  • For big jobs, invoice a deposit first and show it on the final invoice.
  • Agree any late-payment charge in writing before the work starts.

Credit notes: how to fix an invoice you've sent

Once an invoice is issued, don't edit it or reuse its number. If the amount was wrong, goods came back or you gave a discount afterwards, issue a credit note pointing back to the original. For GST-registered businesses, IRAS lists what it must show: a credit note number and date, the original tax invoice's number and date, your details and the customer's, what's credited, the amount, the GST rate, the GST credited and the total.

The GST adjustment usually goes in the GST F5 return for the period the credit note is issued in. If the whole invoice was wrong, credit all of it and issue a new one with a new number.

A worked example

A made-up aircon servicing business that isn't GST-registered, top to bottom. Keep the order and swap in your details:

  • Header: Invoice · Cool Breeze Aircon Services · your UEN, address, phone and email.
  • Invoice no. INV-0042 · Date 4 November 2026 · Your PO: PO-7781.
  • Bill to: Lim Property Management Pte. Ltd., attention Accounts, with their address.
  • General servicing, wall-mounted unit · 4 × S$25.00 = S$100.00.
  • Chemical wash, 12,000 BTU unit · 1 × S$80.00 = S$80.00.
  • Gas top-up (R32) · 1 × S$60.00 = S$60.00.
  • Total S$240.00 · Deposit paid S$0.00 · Balance due S$240.00.
  • Please pay by 18 November 2026 by PayNow to our UEN, quoting INV-0042.

The same invoice with GST

If the business were GST-registered, the title would read 'Tax Invoice', its GST number would sit under the UEN, and the totals would read: total excluding GST S$240.00, GST at 9% S$21.60, total including GST S$261.60. Singapore's GST rate has been 9% since 1 January 2024. For orders with purchase orders and delivery orders too, see our guide to delivery orders vs invoices.

How AQUORIA O.N.E makes receipts and A4 invoices

Every order or job in AQUORIA O.N.E prints as a narrow receipt for the counter or a full-page A4 invoice, and both save as a PDF. The document names itself: 'Receipt' once paid, 'Invoice' while money is owed, and 'Tax invoice' when you've entered your GST registration number and charged GST. Receipts and A4 invoices are on both Essential and Business.

An A4 invoice starts as a draft with no number or pay-by date. When the amount is final, press Issue invoice: it takes the next number in your series, such as INV-0042, and keeps it. The pay-by date comes from your payment terms, or a business customer's own terms.

It shows your logo, business name, address, registration and GST numbers; the invoice number, date, pay-by date and the customer's PO number; and a bill-to box with the customer's name or business name, registration and tax numbers and billing email (not their postal address, which IRAS asks for on a full tax invoice). Then the lines, subtotal, discount, GST at its rate, total, payments and balance due.

Under 'How to pay' it prints your payment note, such as bank details, and in Singapore a PayNow QR for the exact balance, referenced with the invoice number. The Invoices page shows each invoice as paid, unpaid or overdue and downloads as a spreadsheet for your accountant. A credit note gets its own number, such as INV-CN-0001, shows the original invoice's number and date, the reason and the GST in it, and either refunds the money or comes off what's owed.

How it works

  1. 1Enter your UEN and, if registered, your GST number in Settings, and choose how invoice numbers start.
  2. 2Set your payment terms, payment note and PayNow UEN or mobile number.
  3. 3Open A4 invoice on a finished job, check the draft and press Issue invoice.
  4. 4Save it as a PDF and send it; the PayNow QR asks for the exact balance.
  5. 5Follow up what's overdue on the Invoices page, and credit-note any mistakes.

What you'll use

Plan: Essential or Business

Sources

Published 4 November 2026

Questions

What must be included in an invoice in Singapore?

Your business name, UEN and contact details, the word 'Invoice', a unique number, the date, the customer's name, each item with its quantity and price, the total, and when and how to pay. If you're GST-registered and charge GST, IRAS's tax invoice rules add your GST number, the customer's address, the GST rate and amount, and totals before and after GST.

Can I issue an invoice without GST in Singapore?

Yes, if you aren't GST-registered, which most new businesses aren't. Leave out the GST line, don't call it a tax invoice and don't add 9%: IRAS doesn't allow unregistered businesses to charge GST. Registration becomes compulsory once taxable turnover passes S$1 million in a calendar year, or is expected to within the next 12 months.

What is the difference between an invoice and a tax invoice?

An invoice is any bill asking to be paid. A tax invoice is the document a GST-registered business issues when it charges GST, and IRAS sets what it must show: the words 'Tax Invoice', the supplier's GST number, the customer's name and address, the GST rate and amount, and totals with and without GST. Only GST-registered businesses issue them.

How do I number my invoices?

Use one running sequence that never repeats, such as INV-0001, INV-0002 and so on. Don't reuse a number after cancelling an invoice, and don't delete issued invoices; correct them with a credit note in its own series. A short prefix is fine, but keep dates and customer names out of the number itself.

How do I correct an invoice that has already been sent?

Issue a credit note instead of editing the invoice. It gets its own number and date, refers to the original invoice's number and date, and says what's being credited and why. If you're GST-registered, it also shows the GST rate and the GST credited. If the whole invoice was wrong, credit it in full and issue a new invoice with a new number.

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