What an invoice should contain
An invoice is a request for payment. At a minimum it should show who is billing and who is being billed, an invoice number and date, a description of what was supplied, the amounts with GST shown clearly, the total due, when payment is due, and how to pay. Clear payment details at the foot are what actually get you paid on time.
How an invoice differs from a quotation
A quotation comes first: an offer to do work at a stated price, with a validity period. An invoice comes after: a request for payment, with a due date. The same line items usually carry through, which is why keeping your quote tidy saves time when you bill. Our quotation generator shares the same business, customer and line-item records with this tool.
Payment terms: what gets paid faster
"Due on receipt" sets the expectation that payment is immediate. "Net 7", "Net 14" and "Net 30" give the customer 7, 14 or 30 days. Shorter terms tend to get paid sooner, but match them to your customer: a large company on Net 30 will pay on its own cycle regardless. State the due date plainly, and put your bank or PayNow details where they cannot be missed.
Deposits already paid, and showing the balance
If the customer paid a deposit at quotation, show it. Record the amount already paid and the invoice shows the remaining balance due, prominently, so there is no confusion about what is still owed. This is the common case when an accepted quote with a deposit becomes an invoice.
Stating GST plainly
If your prices exclude GST, show GST as its own line. If they include GST, say the total is GST-inclusive. Leaving it unstated is the most common invoicing dispute. This tool pulls the current GST rate for you and shows the treatment in words. It applies GST to the sum of all line values excluding GST, and rounding may differ slightly from an item-by-item calculation.
Tax invoices
If you are GST-registered and billing another GST-registered business, you generally have to issue a tax invoice, and IRAS specifies particulars it must contain, including the words "Tax Invoice", your GST registration number, the customer's name and address, and the GST shown separately. A tax invoice is generally required within 30 days of the supply, and both parties should keep it for at least 5 years. When you tick that both you and your customer are GST-registered, this tool titles the document "Tax Invoice" and includes those particulars; otherwise it produces a plain invoice.
This tool does not handle customer accounting tax invoices. If your supply is subject to customer accounting, follow the IRAS guidance.
Keeping invoice numbers sequential
Sequential numbering keeps your records auditable. Gaps read as missing invoices; duplicates read as double-billing. Both cause problems at tax time. This tool auto-increments your number and warns, but does not block, if you reuse one you have saved before.
Singapore's InvoiceNow shift
Singapore is changing how GST-registered businesses send invoice data to IRAS, through a network called InvoiceNow. If you are still making invoices by hand, it is worth knowing when it applies to you. Check your InvoiceNow deadline →
Common questions
What should an invoice contain?
Who is billing and who is being billed, an invoice number and date, a description of what was supplied, the amounts with GST shown clearly, the total due, a due date, and how to pay. If you are GST-registered and billing another GST-registered business, a tax invoice has extra required particulars set by IRAS.
How is an invoice different from a quotation?
A quotation is an offer before work is agreed, with a validity period. An invoice is a request for payment after, with a due date. The same line items usually carry through.
Does my logo or customer data get uploaded anywhere?
No. Everything, including your logo and payment details, is stored in your own browser. The PDF is built on your device. Nothing you enter is sent to any server.
Why keep invoice numbers sequential?
It makes your records auditable. Gaps look like missing invoices and duplicates look like double-billing. This tool auto-increments and warns if you reuse a number.
Should GST be shown as inclusive or exclusive?
Either, but state which plainly. If prices exclude GST, show GST as its own line. If they include GST, say the total is GST-inclusive.
Where to check
For the tax-invoice particulars and record-keeping rules, the authoritative source is IRAS.