GST Calculation in Singapore: How to Add, Remove and Claim Input Tax With Examples

How much GST should you charge on a $1,000 invoice — and how much can you claim back on your expenses? If you paused on either question, you're in good company: GST calculation in Singapore is simple maths wrapped in rules that catch out plenty of founders.

Goods and Services Tax (GST) in Singapore has sat at 9% since 1 January 2024. The Inland Revenue Authority of Singapore (IRAS) administers it, and registered businesses must charge, collect and report it correctly on every taxable sale.

The stakes are real. A late GST F5 return draws an automatic $200 penalty under IRAS rules, and claiming input tax you're not entitled to creates a costlier mess to unwind later. Getting the sums right the first time is far cheaper.

In this blog, we discuss the formulas for adding and removing GST, what the numbers mean on your GST F5 return, which input tax you can claim, and the 2026 filing deadlines.

What Is GST and What Is the Current Rate in Singapore?

GST is a consumption tax on most goods and services sold in Singapore, charged at 9% since 1 January 2024.

If you sell a taxable product for $100 before tax, you add $9 of GST. Your customer pays $109, you keep $100, and the $9 belongs to IRAS until you file your return. That's the whole system in one sentence.

The rate rose from 8% to 9% on 1 January 2024, so any guide still using 7% or 8% is out of date. Every formula in this article uses the current 9%.

1. Who has to charge GST

Only GST-registered businesses may charge GST from their effective registration date. Registration is compulsory if taxable turnover exceeds $1 million at the end of a calendar year or is expected to exceed $1 million in the next 12 months, subject to limited exceptions. Below it, you may still register voluntarily. For a startup business, the decision to register voluntarily often hinges on whether input tax claims would outweigh the compliance burden.

2. What the 9% applies to

Most local supplies of goods and services attract 9%. Exports and qualifying international services are zero-rated, while supplies such as residential property rentals and most financial services are exempt — you don't charge GST on them, but you also can't claim input tax on their related costs. For businesses holding digital assets, getting the accounting treatment for cryptocurrencies and NFTs right matters just as much as getting GST right.

3. Why the rate drives every formula

A rate of 9% gives you two magic numbers: 1.09 when you add GST to a net price, and 109 when you work backwards from a GST-inclusive price. Keep those in mind and the rest of this article is straightforward.

How Do You Add GST to a Price?

Multiply the net price by 1.09 for the GST-inclusive total, or by 0.09 to find the GST amount on its own.

Adding GST always starts from the net — the price before tax. Multiply that price by 0.09 to get the GST, or by 1.09 to jump straight to the total your customer pays.

Say you're invoicing $1,000 for consulting work. The GST is $1,000 × 0.09 = $90, and the invoice total is $1,090. Your tax invoice should show the net amount, the GST and the total as separate lines.

1. The formula for adding 9% GST

GST amount = net price × 0.09. GST-inclusive price = net price × 1.09. Use the first formula for the GST figure and the second for the total price.

2. Worked example: a $1,500 invoice

Net $1,500 × 0.09 = $135 GST. The invoice total is $1,635. On the GST F5 return, $1,500 goes in Box 1 and $135 in Box 6 — never $1,635 in Box 1.

3. Common mistakes when adding GST

The usual slips include:

• Charging GST before your registration is active
• Rounding the GST to the wrong cent
• Omitting the GST line on a tax invoice
• Leaving old prices in your system without the new rate

For rounding: compute GST on each line item to the nearest cent, rounding 0.5 cents up; where multiple items appear on one invoice, total the unrounded line-item GST first and round that total to the nearest cent.

The compliance risk varies by mistake — charging before registration and omitting the GST line tend to attract the most attention from IRAS — so check your invoice template once and let your accounting software handle the rest.

How Do You Remove GST From a Price?

Divide the GST-inclusive price by 1.09 to get the net amount, then subtract the net from the gross to reveal the GST portion.

You'll need this whenever a supplier sends a GST-inclusive bill, you record expenses, or you price backwards from a target all-in figure. The division matters because the gross figure already contains the tax — you can't simply take 9% of it.

Take a $218 receipt from a GST-registered supplier. $218 ÷ 1.09 = $200 net, and $218 − $200 = $18 of GST. That $18 is the input tax you may be able to claim.

1. The formula for removing 9% GST

Net amount = gross ÷ 1.09. GST portion = gross − net amount. Two steps, no more.

2. The trap of taking 9% of the gross

9% of $218 is $19.62 — but that's wrong, because 9% of a GST-inclusive figure overstates the tax. The correct GST inside $218 is $18. Using the wrong method overclaims input tax and skews your F5 return.

3. When you actually need to do this

Removing GST comes up when recording GST-inclusive expenses in Xero, checking a supplier's tax invoice, or working out the net price behind a target all-in quote.

How Does GST Calculation Flow Into Your GST F5 Return?

Every figure you calculate lands in a labelled box on your GST F5 return, which IRAS requires you to e-File within one month of your accounting period's end.

IRAS sets out the mechanics in its e-Tax Guide on preparing your GST return, most recently updated on 30 January 2026. In short: Box 1 holds the value of your standard-rated supplies excluding GST, Box 6 holds output tax due, Box 7 includes input tax and other GST refunds claimed, and Box 8 is the net GST payable or refundable.

The maths is exactly what this article covers. Sell $1,000 of services plus $90 GST, and Box 1 shows $1,000 while Box 6 shows $90. The guide is explicit that Box 1 excludes the GST amount.

File late and IRAS immediately imposes a $200 late-submission penalty, with a further $200 for each completed month outstanding up to $10,000. IRAS may grant a two-week extension in specified exceptional circumstances if you apply at least five working days before the due date and provide the required supporting documents. Made an error? You may adjust it in your next GST F5 only if the net GST error across all affected periods is no more than $3,000 and the non-GST errors meet IRAS's 5% test; otherwise, file GST F7.

1. What each box captures

Box 1 is the value of standard-rated supplies excluding GST. Box 6 is the output tax collected. Box 7 is the input tax and other GST refunds claimed. Box 8 is Box 6 minus Box 7 — the amount payable to, or refundable from, IRAS.

2. Monthly versus quarterly filing

The standard accounting period is quarterly. A business likely to receive GST refunds regularly may apply for monthly accounting periods, subject to IRAS approval; the same one-month filing rule applies either way.

3. Where professional help pays off

Keeping the boxes straight each quarter is routine work for professional tax services, which reconcile your GST account before anything is filed. Many firms, including ours, fold GST reporting into the same monthly package as your bookkeeping.

What Input Tax Can You Claim in Singapore?

You can claim input tax when the purchase is for your business, the supplier is GST-registered, and you hold a valid tax invoice or import document.

Input tax is the GST your suppliers charged you. Claimed properly, it cuts what you pay IRAS each quarter, so it's worth knowing the boundaries.

In practice, we check every client's claim against the same short list before it touches the F5. Reliable bookkeeping services make that review easier by keeping the supporting records together. The conditions below come straight from IRAS's expectations for a valid claim.

1. The conditions for a valid claim

IRAS expects all of the following before input tax can be claimed:

• The purchase is for your business, not personal use
• The purchase relates to your taxable supplies, not exempt or private activities
• The supplier is GST-registered
• You hold a valid tax invoice or import permit
• You claim in the correct accounting period

2. Purchases IRAS does not allow

Some costs are blocked outright, with very limited exceptions. The list includes:

• Passenger cars, except where IRAS specifically permits a claim (for example, taxis and driving-instruction vehicles)
• Club and similar membership fees
• Goods or services bought for personal consumption

Claiming on these is one of the fastest ways to invite a review, so it's worth screening expenses before each quarter closes.

3. Record-keeping that survives scrutiny

Keep tax invoices and supporting records for at least five years. This is where reliable bookkeeping services earn their keep — our daily bookkeeping on Xero captures every tax invoice as it's issued and received, so nothing is claimed twice or missed.

When Are Your GST Filing Deadlines in 2026?

Quarterly filers face four deadlines a year, each falling one month after the end of the accounting period.

IRAS lists the official due dates for 2026, and extensions are available only in specified exceptional circumstances. You must apply at least five working days before the filing due date and provide the required supporting documents. Payment of any net GST is due by the same date as the return, so diarise both together.

Quarterly filers with periods ending in 2026 file as follows:

• Period ending March 2026 — due 30 April 2026
• Period ending June 2026 — due 31 July 2026
• Period ending September 2026 — due 31 October 2026
• Period ending December 2026 — due 31 January 2027

Getting the GST account right also feeds into your Singapore year-end close, when the GST account is reconciled against the returns you've filed. The same year-end figures then support compilation of financial statements for filing.

Conclusion

Here's the whole article in three lines: add GST by multiplying the net price by 1.09, remove it by dividing the gross by 1.09, and claim input tax only on valid, business-related purchases backed by tax invoices. All of it flows into your GST F5 return, due within one month of every period end.

In practice, the maths is rarely the hard part — the record-keeping is. That's why we run daily bookkeeping on Xero for our clients, tracking every invoice and expense as it happens so your GST boxes fill themselves. Quarterly GST submission is available as an add-on at $100 per month, billed annually, as published on our pricing page.

When you work with Single Point Contact, you get one dedicated point of contact on WhatsApp, and we handle your GST reporting, tax filings and year-end numbers so nothing lands on your desk. That's GST calculation in Singapore, taken care of.

Frequently Asked Questions