How to Invoice Customers in Singapore the Right Way (and Stay GST-Compliant)

If you’ve ever had a GST claim rejected because of a small invoicing mistake, you know how painful it can be.

Maybe you forgot to include your customer’s GST registration number. Maybe you didn’t issue the invoice within the 30-day limit. Or perhaps, your foreign currency invoice didn’t show the correct conversion to Singapore dollars.

Sounds familiar? You’re not alone.

Many Singapore businesses—especially SMEs—still underestimate how important proper invoicing is. It’s not just paperwork. It’s compliance, cash flow, and credibility all rolled into one.

In this guide, we’ll walk you through exactly how to invoice customers in Singapore the right way, from understanding the types of invoices to avoiding common pitfalls that could get you in trouble with IRAS.

Key Takeaways

Proper invoicing isn’t just an accounting chore—it’s a compliance safeguard and a trust-building tool.

Here’s a quick recap of what matters most:

Issue tax invoices within 30 days for GST-registered customers.
Include all mandatory details as required by IRAS.
Use approved exchange rates when invoicing in foreign currencies.
Apply consistent GST computation and rounding methods.
Keep all invoices for 5 years, whether issued or received.
Use customer accounting invoices when required for prescribed goods.
Consider adopting Peppol e-invoicing for efficiency and accuracy.

Why Tax invoices matter more than you think

If you’ve ever lost hours fixing invoice errors or waiting on delayed payments, you’ve already seen why tax invoices are mission-critical.

In Singapore, a tax invoice isn’t just a receipt. It’s the main document that supports a business’s input tax claim under the Goods and Services Tax (GST) system.

That means:

Your customer needs a proper tax invoice to claim input tax.
You, the supplier, must issue and retain that invoice as proof of your taxable supply.

Without it, your customer can’t claim GST—and you could face compliance penalties during an IRAS audit.

Think of it as the DNA of every transaction. It contains all the details that prove a sale occurred, including the amount of GST charged and who’s responsible for what.

What exactly is a tax invoice

A tax invoice (or customer accounting tax invoice) is a formal document issued when you make a taxable supply to a GST-registered customer.

It includes key information such as your business details, the GST amount, and the type of supply made.

You must:

Issue a tax invoice within 30 days from the time of supply.
Retain copies of all invoices you issue and receive for at least 5 years.
Use these invoices as records but not submit them with your GST returns.

In short: Tax invoices are the backbone of your GST records, not something you can afford to overlook.

When to Issue (and When Not To)

Here’s where things get tricky for many businesses.

You must issue a tax invoice when:

Your customer is GST-registered.
The sale involves standard-rated supplies.
You’ve made the supply, and payment is due.

You don’t need to issue a tax invoice when:

The supply is zero-rated, exempt, or deemed.
Your customer is not GST-registered.
The transaction involves deposits under the Beverage Container Return Scheme (BCRS), since these are not subject to GST.

However, even for BCRS-related sales, IRAS encourages businesses to include deposits in tax invoices for price transparency. It’s a good practice for building customer trust.

The takeaway?
👉 Always know your customer’s GST registration status before issuing an invoice. It determines the kind of document you need to send.

What information must appear on a tax invoice?

IRAS requires specific information to be included on every tax invoice:

The words “Tax Invoice” are prominently displayed
Supplier’s name, address, and GST registration number
Invoice date and unique invoice number
Customer’s name and address
Description of goods or services supplied
Quantity and total value (excluding GST)
GST amount charged
Total amount payable (including GST)

If your invoice involves multiple types of supplies (standard-rated, exempt, or zero-rated), you must separately state the gross amount for each type.

That level of detail isn’t optional—it’s mandatory. Missing or incomplete information could invalidate the document for GST purposes.

Rounding off GST and Total Bills

Another small but often overlooked detail: rounding.

You can round the total GST on all goods and services to the nearest cent (two decimal places).

If you’re dealing with cash payments, you may also round the total bill (including GST) to the nearest 5 cents—a practical adjustment to facilitate payments.

Whether you choose to round up or down is your business decision. The only rule is: apply it consistently. Inconsistent rounding practices could create mismatched figures between your sales records and GST returns.

Let’s say Urban Brew Café, a small coffee chain in Singapore, sells a latte at $4.68 before GST.

GST (9%) = $0.4212 → rounded to $0.42
Total payable = $4.68 + $0.42 = $5.10

When the café issues an invoice for multiple items, the total GST may be rounded to the nearest cent, and the final bill may be rounded to the nearest 5 cents (e.g., $18.92 → $18.90) to simplify cash handling.

As long as Urban Brew Café applies this method consistently across all transactions, IRAS will consider it compliant.

When to issue a customer accounting tax invoice?

Here’s a special case:

When you make a relevant supply subject to customer accounting, you must issue a customer accounting tax invoice instead of a regular tax invoice.

This happens for certain prescribed goods, such as:

Mobile phones
Memory chips
Precious metals

In these transactions, your GST-registered customer is responsible for accounting for both output and input tax.

That means:

You issue a customer accounting tax invoice, not a regular one.
Your customer reports the GST on your behalf in their return.
This system helps IRAS reduce tax evasion in high-value, easily resold goods.

For details on what to include in a customer accounting tax invoice, refer to the official GST: Customer Accounting for Prescribed Goods e-Tax Guide from IRAS.

Simplified Tax Invoices (Under $1,000)

Not every sale needs a full-blown tax invoice.

If the total payable (including GST) does not exceed $1,000, you can issue a simplified tax invoice instead.

It must include:

Supplier’s name, address, and GST number
Date of issue
Invoice number or identifying reference
Description of goods/services
Total amount payable (including GST)
A statement such as “Price payable includes GST”

Sales vouchers or debit notes can double as simplified tax invoices if they contain all these details. Simplified invoices save time for small-value transactions but still keep your business compliant.

Pro tip: Keep everything for 5 years

IRAS requires all tax invoices—issued and received—to be kept for at least 5 years.

That means even if you switch software systems, merge with another company, or close your GST account, you must still retain copies for audit purposes.

Digital storage (such as e-invoicing through the Peppol Network) is perfectly acceptable as long as records are complete and retrievable.

Singapore is moving fast toward a fully digital invoicing ecosystem.

Through the Peppol e-invoicing network, businesses can send invoices directly between accounting systems in a secure, structured format recognized by IRAS.

Benefits include:

Reduced manual data entry and errors
Faster processing and payment cycles
Stronger record-keeping for audits
Seamless integration with GST reporting
Even though e-invoicing is still optional for many, early adoption gives your business a serious edge in compliance and efficiency.

Final Thoughts

Invoicing the right way in Singapore isn’t about bureaucracy—it’s about running a professional, compliant business.

A well-structured invoice does more than secure payment; it reflects how seriously you manage your operations. It tells clients you’re reliable, transparent, and audit-ready.

The best part? Once you build a clear system, compliance becomes effortless.

So the next time you send an invoice, don’t just hit “send” or print it right away— make sure it’s GST-perfect. Your accountant, your customers, and IRAS will thank you for it.

If your company needs help filing taxes for the year 2025 or requires assistance with Singapore incorporation, economy, banking, etc., feel free to call /WhatsApp us at +65 90612851 or email us at aceglobalacct@gmail.com. Alternatively, you may leave us a reply using our contact form below.

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