Below: who issues each document, what it should show, what IRAS requires on a tax invoice if you're GST-registered, the flow from order to payment, and how AQUORIA O.N.E produces each one.
The five documents at a glance
- Purchase order (PO): issued by the buyer to the supplier, before anything is delivered. It lists the items, quantities, agreed prices, the delivery address and a PO number. Once the supplier accepts it, it's the order both sides work from.
- Delivery order (DO): issued by the supplier and sent with the goods. It lists what was delivered and for which order or PO, and the receiver signs it to say the goods arrived in good order. It usually shows no prices.
- Invoice: issued by the supplier after delivery or after the work is done. It asks for payment: what was supplied, the price, any GST, the total and when it's due.
- Receipt: issued by the seller when money comes in. It proves the customer paid, how much and when.
- Statement of account: issued by the supplier, usually monthly, to customers who buy on credit. It shows what was owed at the start of the month, what was charged, what was paid and what's owed now.
The flow from order to payment
Picture a line from left to right, with the buyer on top and the supplier underneath. Each arrow is one document changing hands:
- 1. Purchase order: the buyer sends a PO, and the supplier checks stock and confirms.
- 2. Delivery order: the supplier delivers the goods with a DO; the buyer checks them and signs, and the supplier keeps the signed copy as proof of delivery.
- 3. Invoice: the supplier invoices, showing the buyer's PO number, and the buyer matches PO, DO and invoice (the three-way match) before paying.
- 4. Receipt: the buyer pays, and the supplier issues a receipt or marks the invoice paid.
- 5. Statement: at month end, the supplier sends a statement of every invoice and payment, and the buyer settles anything still owed.
When you need all five, and when you don't
For a walk-in customer, steps 1, 2 and 5 drop away: there's a sale and a receipt. For a café that takes bread from a bakery every morning on 30-day terms, every step is used, every day. The more a customer buys on credit, the more these papers protect you: a signed DO settles 'we never got it', and a statement settles 'we thought we'd paid'.
What an invoice must show in Singapore
If you're not GST-registered, IRAS's tax invoice rules don't apply to you, but a clear invoice shows your business name and UEN, an invoice number, the date, the customer's name, what was supplied with quantities and prices, the total, and how and when to pay. Until you're registered you must not charge GST or call your bill a tax invoice.
If you're GST-registered, IRAS sets what a tax invoice must show, all on one document:
- The words 'Tax Invoice', shown clearly.
- Your name, address and GST registration number.
- An invoice number and the date of issue.
- The customer's name and address.
- A description of the goods or services.
- The GST rate, the total before GST, the GST amount and the total including GST.
Simplified tax invoices, receipts and the 30-day rule
A tax invoice must reach a GST-registered customer within 30 days of the supply. For a supply of S$1,000 or less including GST, IRAS allows a simplified tax invoice without the customer's details, showing the total including GST and a statement that the price includes GST. A customer who isn't GST-registered can be given a receipt instead: serially numbered, with your name, GST registration number, the date, the total including GST and a note that the price includes GST. If you invoice in a foreign currency, the GST figures must be converted into Singapore dollars.
What a PO, DO and statement should show
- Purchase order: PO number and date, the supplier, your delivery address, item codes, quantities, agreed unit costs, the total, and any note such as 'deliver before 9am'.
- Delivery order: DO number, the order or PO it belongs to, the delivery address, items and quantities, and a box for the receiver's name, signature and date.
- Statement: the customer's name, the month, what was owed at the start, each invoice charged, each payment received, what's owed at the end, and the due date.
How AQUORIA O.N.E produces each one
Receipts and invoices (Essential and Business): every order prints or saves as a PDF. A paid order prints as a receipt; one with money still owed prints as an invoice; once you enter your GST registration number and charge GST, it's titled Tax invoice. The A4 invoice shows your business and registration numbers, the invoice number and date, the bill-to customer, description, quantity, unit price, subtotal, GST at its rate, total, what's paid, the balance due, the pay-by date and a PayNow QR for the balance. An invoice can stay a draft, with no number, until the work and amount are final; then you issue it. If an issued invoice needs correcting, you issue a credit note against it.
Purchase orders (Business): pick a supplier and items, and the PO is made with its number, your delivery address, item codes and unit costs, plus a line asking the supplier to show the PO number on their DO and invoice. Download it as a PDF, email it from your own connected mailbox, or tap WhatsApp to open a chat with the supplier on your phone with the message and link written. When goods arrive, 'Goods received' adds them to stock and records the cost under Expenses; part deliveries are tracked until the rest comes or you close the PO.
Delivery orders (Business): a trade order gets a DO with its number, the customer's PO, what went and where, and a 'Received in good order and condition' box for name, signature and date. When your driver takes the signature on delivery, the DO shows it as signed on delivery.
Business accounts and statements: mark a trade customer as a business account with a credit limit, payment terms such as 30 days, their own prices, and 'Purchase order number required' if they always send one. Their PO number prints on your invoice and DO, and you can attach their PO file to the order. Each month their statement shows what was owed at the start, charged, paid and owed at the end, with a due date, ready to email. The invoice list shows what's paid, unpaid or overdue, and exports to a spreadsheet for your accountant.
How it works
- 1On Business, add your suppliers and send a purchase order for the stock you need.
- 2Take the customer's order, with their PO number if they use one.
- 3Deliver with a delivery order and get it signed.
- 4Issue the invoice; the customer pays by PayNow or transfer and gets a receipt.
- 5Send the monthly statement and follow up what's overdue.
What you'll use
- InvoicingInvoice software for Singapore: receipts and A4 invoices with GST, numbering, payment terms, PayNow QR, statements and reminders. Free for 14 days.
- Purchase ordersBusinessPurchase order software for Singapore: low stock to PO in one tap, POs as PDF, goods received into stock, supplier invoice PDFs read into bills. Try free.
- Wholesale ordersBusinessWholesale software for Singapore: trade accounts with own prices, credit limits and POs, standing orders, delivery orders and monthly statements. Try free.
- Delivery managementDelivery management system for Singapore: time windows customers pick, routes by time and area, and a driver app with photo or signature proof. Try free.
- AccountingAccounting software for Singapore: expenses and profit, bills to pay, bank matching from your statement, GST F5 figures and CSV exports. Try it free.
Plan: Essential or Business
Sources
- IRAS: Invoicing customers (GST)
- IRAS: Responsibilities of a GST-registered business
- IRAS: GST General Guide for Businesses
- IRAS: Do I need to register for GST?
- IRAS: Keeping proper records and accounts (self-employed)
Published 4 November 2026
Questions
What is the difference between a delivery order and an invoice?
A delivery order goes with the goods and lists what was delivered; the customer signs it as proof the goods arrived. An invoice asks for payment and shows prices, any GST, the total and when it's due. The DO usually comes first, at delivery, and the invoice follows, often showing the same order or PO number.
What is the difference between a purchase order and an invoice?
A purchase order comes from the buyer and says what they want to buy, at what price. An invoice comes from the supplier after delivery and asks to be paid. Matching the two, along with the signed delivery order, is how the buyer checks they're paying only for what they ordered and received.
Is an invoice the same as a receipt?
No. An invoice asks for payment; a receipt proves payment was made. A cash sale at the counter usually only needs a receipt. A sale on credit gets an invoice first and a receipt, or an invoice marked paid, once the money arrives. Keep both: IRAS asks self-employed people to keep records for five years.
What must a tax invoice show in Singapore?
If you're GST-registered, IRAS requires the words 'Tax Invoice', your name, address and GST registration number, an invoice number and date, the customer's name and address, a description, the GST rate, the totals before and after GST, and the GST amount. For S$1,000 or less including GST, a simplified tax invoice is allowed.
Can I issue an invoice without GST in Singapore?
Yes. If you're not GST-registered, your invoice simply has no GST line, and you must not charge GST or call it a tax invoice. Registration becomes compulsory when taxable turnover goes over S$1 million in a calendar year, or is expected to within the next 12 months, so check each year as you grow.
Who signs a delivery order?
The person who receives the goods signs the delivery order, with their name and the date, to confirm the goods arrived in good order. The supplier keeps the signed copy as proof of delivery. If anything is short or damaged, the receiver should note it on the DO before signing, so the invoice can be corrected.