GST Calculator

Adding and removing GST

Goods and Services Tax in Singapore is 9%. That rate has applied since 1 January 2024, after two increases in consecutive years: it was 7% from mid-2007 to the end of 2022, then 8% for the whole of 2023.

There are two directions people need. Adding GST to a price before tax is simple multiplication. Taking GST back out of a price that already includes it is not: you cannot subtract 9% from a GST-inclusive figure, because the tax was calculated on the smaller amount underneath. The right operation is to multiply the inclusive amount by 9/109.

How the arithmetic works

1. Decide whether the figure you have is before GST or already includes it. Displayed prices in Singapore are generally GST-inclusive, so a shelf price usually already contains the tax.
2. To add GST, multiply by the rate and add the result.
3. To remove GST from an inclusive price, multiply the inclusive amount by 9/109. What is left is the value of the taxable supply.
4. Check the direction against a known figure before trusting it. A price before tax of a hundred dollars becomes a hundred and nine; a hundred and nine dollars inclusive contains nine dollars of tax and a hundred dollars of value.

The mistake that costs money: subtracting the rate

Taking 9% off a GST-inclusive price gives an answer that is too small, and the error grows with the size of the invoice. On a large contract that difference is real money and it is the single most common GST arithmetic error in Singapore. If you are reconciling a supplier invoice, always extract with the fraction, never by subtraction.

The second common error is treating every supply as standard-rated. Some supplies are zero-rated, meaning they are taxable but the rate is 0% — exported goods and international services are the usual examples. Others are exempt, such as most financial services and the sale or lease of residential property. The difference matters: a business making zero-rated supplies can still claim input tax, and one making exempt supplies generally cannot.

Why your invoice may not match

Only a GST-registered business may charge GST at all. If a supplier is not registered, there is no tax on the invoice however the price is described, and a business that charges GST without being registered is collecting it wrongly.

Rounding is the other reason for small differences. This calculator works to the cent on a single amount, while accounting systems apply their own rounding at line or invoice level and may total the rounded lines rather than rounding the total. On long invoices those choices produce differences of a few cents that are not errors.

Common questions

Is the displayed price meant to include GST? For most retail supplies, yes. Price displays are generally required to be GST-inclusive so that the amount on the shelf is the amount you pay.

What is the difference between zero-rated and exempt? Both mean no GST is charged to the customer. A zero-rated supply is a taxable supply charged at 0%, and the business can still recover its input tax. An exempt supply is outside the charge and generally carries no input tax recovery.

How do I get the tax out of an inclusive figure? Multiply by 9/109. That fraction is simply the rate over one hundred plus the rate, and it changes whenever the rate changes.

Was GST always this high? No. It was introduced on 1 April 1994 at 3% and has risen five times since, most recently to the current rate.

The GST rate and the treatment of individual supplies are set out by IRAS. Check the current rate and your own registration position with IRAS before you invoice.