To create a professional invoice in Singapore, include your business name and UEN, the client's details, a unique invoice number, the date, a clear description of the work, the amount and currency, your payment terms, and how to pay. Sending your first invoice as a freelancer feels exciting right up until you stare at a blank document wondering what you're actually supposed to include. There's no single law in Singapore that spells out every invoice requirement for non-GST-registered businesses, but there are strong conventions and some legal must-haves if you're GST-registered. Getting your invoice right matters because a professional, complete invoice gets paid faster and avoids awkward back-and-forth with clients.
The good news is that creating a solid invoice isn't complicated once you know what goes where. This guide walks through exactly what to include, how to number your invoices, which payment terms suit which situations, and how to follow up without damaging the relationship.
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Even if you're not GST-registered, there are details every professional invoice should have. Think of this as the baseline your clients expect, and what IRAS might ask about if you're ever audited as a sole proprietor.
- Your business name and address - If you're a registered company, use your registered name. Sole proprietors can use their personal name or trading name. Always include your address or at least a contact address.
- Your UEN (Unique Entity Number) if your business is registered with ACRA. It's not legally required on every invoice, but including it adds credibility and clients often ask for it.
- Client's name and address - Use the legal entity name, not a nickname. This matters for your client's own accounting records.
- Invoice number - Unique, sequential. Never reuse an invoice number.
- Invoice date - The date you're issuing the invoice, not the date you finished the work.
- Description of services or goods - Be specific. "Consulting" is vague. "Brand strategy consulting, 15 hours at $150/hr, April 2026" is what you want.
- Amount due - State the currency clearly, especially if you're working with international clients. SGD 1,500 is unambiguous. $1,500 is not.
- Payment terms - When do you expect payment? Net 30, due on receipt, or a specific date.
- Bank details or payment method - PayNow UEN, bank account number, or however you want to be paid. Don't make clients hunt for this.
If you're GST-registered, you also need to include your GST registration number, label the document "Tax Invoice" clearly, and show the GST amount as a separate line item. There's a full breakdown of GST-specific requirements in our GST invoice guide.
What Are the Best Practices for Invoice Numbering?
Your invoice number does two things: it makes each invoice traceable, and it signals to your clients that you're organised. Sequential numbering is the most common approach and works well for most freelancers. Start at INV-001 and go from there.
Some people prefer date-based formats like INV-2026-001, which makes it easy to see at a glance which year an invoice belongs to. If you work with multiple clients and want to track by client, formats like CLIENT-001 can help. Whatever system you use, the most important rule is simple: never reuse a number, and never skip numbers. Gaps in your invoice sequence can create problems if you're ever asked to account for your income.
You can automate this entirely with IWantFreeInvoice.com - just type in your starting number and increment from there. It takes seconds and you don't need a spreadsheet.
Setting Professional Payment Terms
Payment terms tell your client how long they have to pay. Setting them clearly upfront prevents confusion and gives you a solid basis for following up if a payment runs late.
| Term | What It Means | Best For |
|---|---|---|
| Due on Receipt | Pay immediately upon receiving the invoice | Small one-off jobs, digital deliverables |
| Net 7 | Payment due within 7 days | Urgent services, regular clients |
| Net 14 | Payment due within 14 days | Retainer work, ongoing projects |
| Net 30 | Payment due within 30 days | Large projects, established clients |
| Net 60 | Payment due within 60 days | Corporate clients with fixed payment cycles |
For most freelancers in Singapore, Net 14 or Net 30 is the standard. New clients are usually given Net 14. Established corporate clients sometimes insist on Net 30 or Net 60 because of their internal AP processes - this is normal and not a red flag. If a client pushes for Net 60, you can counter with shorter terms or ask for a deposit upfront to balance your cash flow.
One underrated tip: write out what the terms mean in plain language on the invoice. "Payment due by 14 June 2026" is clearer than "Net 30" and reduces the chance of your client misunderstanding.
How Do You Send Invoices Professionally?
Always send invoices as PDFs. Never send editable documents like Word files or spreadsheets - clients shouldn't be able to change the figures, and PDFs look far more professional. IWantFreeInvoice.com generates a clean PDF you can download and attach in seconds.
The Email Subject Line
A clear subject line saves your client from having to open the email to figure out what it is. Use a format like: Invoice #INV-042 from [Your Name] - SGD 2,400 - Due 15 June 2026. It includes the invoice number, who it's from, the amount, and the due date. Everything they need is in one line.
What to Write in the Body
Keep it short. Something like: "Hi [Client], please find attached Invoice #INV-042 for [service]. Payment of SGD 2,400 is due by 15 June 2026. My bank details are included on the invoice. Let me know if you have any questions." That's it. You don't need multiple paragraphs.
Following Up on Late Payments Without Being Awkward
Late payments happen even with good clients. Having a consistent follow-up process means you don't have to agonise each time over what to write or whether it's too soon.
First Reminder: Friendly and Professional
Send this on or one day after the due date. Assume it was an oversight. Something like: "Hi [Client], just a quick follow-up on Invoice #INV-042 which was due on 15 June. Please let me know if you need me to resend it or if there's anything holding up the payment." Short, no guilt-tripping, easy for them to respond to.
Second Reminder: Firmer
Send this about a week after the first reminder with no response. This one is direct: "Hi [Client], following up again on Invoice #INV-042 for SGD 2,400, now [X] days overdue. Could you let me know when I can expect payment or if there's an issue I can help resolve?" You're still professional but you're making clear this needs action.
Third Reminder: Final Notice
If two weeks have passed with no payment and no explanation, it's time to be explicit. State that you'll be taking further steps if payment isn't received by a specific date. In Singapore, this can mean a formal demand letter or the Small Claims Tribunal for amounts up to SGD 20,000. Most clients pay before it gets to this stage.
The key to all of this is starting early. Freelancers who wait a month before following up give late payers a lot of room. When you use a tool like IWantFreeInvoice.com to send invoices on time with clear payment terms, you set the right expectations from the start and make it easier to follow up when something goes wrong.