GST Calculator Singapore: How to Add and Extract 9% GST

Use this Singapore GST calculator guide to add or extract 9% GST, handle service charges and rounding, and check when your business must register.

TLDR:

Singapore’s current GST rate is 9%, set under the Goods and Services Tax Act 1993.

Multiply a GST-exclusive price by 1.09 to calculate the GST-inclusive total.

Multiply a GST-inclusive price by 9/109 to extract the GST amount.

Apply GST after adding any compulsory service charge.

Round the total GST shown on a tax invoice to the nearest cent.

GST registration generally becomes compulsory when taxable turnover exceeds S$1 million under the retrospective or prospective test.

A GST calculator Singapore businesses can rely on converts prices using the 9% Goods and Services Tax rate set by IRAS under the Goods and Services Tax Act 1993.^[1] A GST-exclusive amount of S$100 therefore produces S$9 of GST and a GST-inclusive total of S$109. A GST-inclusive amount can be reversed by multiplying it by 9/109. The guide below explains both calculations, service charges, discounts, rounding, registration thresholds and the distinction between output tax and input tax.

What is GST in Singapore?

Goods and Services Tax, or GST, is a broad-based consumption tax imposed on imported goods and nearly all supplies of goods and services in Singapore.^[1]

Singapore applies four broad supply classifications: standard-rated supplies, zero-rated supplies, exempt supplies and out-of-scope supplies. Most local sales of goods and services are standard-rated at 9%, while qualifying exports and international services are zero-rated at 0%.^[1]

Exempt supplies include specified financial services, digital payment tokens, the sale and lease of residential properties, and the import and local supply of investment precious metals.^[1] Out-of-scope transactions can include private transactions and sales in which goods move from one overseas location to another without entering Singapore.^[1]

A GST calculator should only apply 9% after the business has determined that the transaction is standard-rated. A mathematically correct calculation can still produce the wrong tax treatment when the underlying supply is zero-rated, exempt or outside the scope of GST.

What is the current GST rate in Singapore?

The current GST rate in Singapore is 9%.^[1]

GST-registered businesses must charge and account for GST at 9% on their standard-rated sales of goods and services in Singapore.^[1] The 9% rate has applied since 1 January 2024.^[1]

A Singapore GST calculator should use 9% for current standard-rated transactions. Historical invoices must use the rate applicable to the transaction under the relevant time-of-supply rules rather than automatically applying the current rate.

How do you calculate GST in Singapore?

Businesses calculate GST by first identifying whether the starting amount includes GST and then applying the corresponding 9% formula.^[1]

Confirm the supply type. Determine whether the transaction is standard-rated, zero-rated, exempt or out of scope before performing the calculation.
Identify the starting amount. Establish whether the quoted figure is GST-exclusive or GST-inclusive.
Include taxable additions. Add compulsory service charges or other taxable fees before calculating GST where applicable.^[3]
Apply the correct formula. Use 9% of the net amount to add GST, or use the 9/109 tax fraction to extract GST from an inclusive amount.^[2]
Round the GST amount. Round the total GST shown on the tax invoice to the nearest whole cent, meaning two decimal places.^[4]
Record each component. Keep the GST-exclusive value, GST amount and GST-inclusive total separately in the accounting records.

Which GST formula should you use?

The correct formula depends on whether the known price excludes or includes GST.

Calculation	Formula at 9%	Example	Result
GST on a GST-exclusive price	Net price × 9%	S$1,000 × 0.09	S$90 GST
GST-inclusive total	Net price × 1.09	S$1,000 × 1.09	S$1,090 total
GST extracted from an inclusive price	Gross price × 9/109	S$1,090 × 9/109	S$90 GST
Net price extracted from an inclusive price	Gross price ÷ 1.09	S$1,090 ÷ 1.09	S$1,000 net

The tax-fraction method is necessary because 9% of the GST-inclusive total is not the GST component. GST forms 9 parts of a 109-part total when a net price of 100 parts attracts 9 parts of tax.^[2]

How do you add GST to a price?

Multiply the GST-exclusive price by 1.09 to obtain the GST-inclusive price.

For a GST-exclusive invoice value of S$2,400:

GST amount: S$2,400 × 9% = S$216
GST-inclusive total: S$2,400 + S$216 = S$2,616
Equivalent one-step calculation: S$2,400 × 1.09 = S$2,616

A calculator with GST may display both the tax and final amount, but finance teams should retain the original GST-exclusive value as a separate figure. Separate values make invoice checking and accounting reconciliation easier.

How do you extract GST from an inclusive price?

Multiply a GST-inclusive price by 9/109 to extract the GST component.^[2]

For a GST-inclusive total of S$5,450:

GST amount: S$5,450 × 9/109 = S$450
GST-exclusive value: S$5,450 − S$450 = S$5,000
Equivalent net calculation: S$5,450 ÷ 1.09 = S$5,000

Multiplying S$5,450 by 9% would produce S$490.50, which is incorrect because the starting amount already contains GST. The 9/109 tax fraction isolates the 9 parts of tax contained within the 109-part gross price.

How is GST calculated when a service charge applies?

GST is calculated on the total price payable after adding a compulsory service charge. IRAS states that the service charge is subject to GST because it forms part of the total price for the goods and services provided.^[3]

A S$2,500 bill with a 10% service charge is calculated as follows:

Service charge: S$2,500 × 10% = S$250
Subtotal before GST: S$2,500 + S$250 = S$2,750
GST: S$2,750 × 9% = S$247.50
Final amount: S$2,750 + S$247.50 = S$2,997.50

The shortcut for a price subject to both a 10% service charge and 9% GST is base price × 1.10 × 1.09. The combined increase is 19.9%, rather than 19%, because GST also applies to the service-charge amount.

How is GST calculated after a discount?

GST is generally calculated on the reduced selling price when a discount lowers the consideration payable for the supply.

For an item priced at S$500 before a 10% discount:

Discount: S$500 × 10% = S$50
Discounted price: S$500 − S$50 = S$450
GST: S$450 × 9% = S$40.50
GST-inclusive total: S$450 + S$40.50 = S$490.50

The calculation order matters. A finance team should apply the commercial adjustment first and calculate GST on the resulting taxable amount. Credit notes, rebates, vouchers and bundled promotions can require more detailed analysis because the contractual arrangement determines the consideration for the supply.

How should businesses round GST?

Businesses may round the total GST payable on all goods and services shown on a tax invoice to the nearest whole cent, meaning two decimal places.^[4]

A calculated GST amount of S$11.376 becomes S$11.38 when rounded to two decimal places. A calculated amount of S$11.374 becomes S$11.37.

Businesses should configure invoicing and accounting systems to use one documented method consistently. Differences can arise when software rounds GST for every line item instead of calculating GST on the combined taxable value and rounding the total. Finance teams should investigate recurring one-cent differences rather than manually overwriting entries without an audit trail.

Which transactions should a GST calculator exclude?

A standard 9% goods and services tax calculator should exclude transactions that are zero-rated, exempt or outside the scope of GST.^[1]

Supply type	GST treatment	Common examples	Calculator action
Standard-rated	9% GST	Most local sales of goods and services	Apply the 9% add or extract formula
Zero-rated	0% GST	Qualifying exports of goods and international services	Record as taxable at 0%; do not add 9%
Exempt	GST is not chargeable	Specified financial services, digital payment tokens, residential property transactions and investment precious metals	Do not add 9%
Out of scope	Outside Singapore GST	Certain private transactions and overseas-to-overseas sales	Do not add 9%

Zero-rated supplies remain taxable supplies even though the applicable rate is 0%.^[1] Exempt supplies differ because GST is not chargeable, and the related input-tax treatment can also differ from the treatment of taxable supplies.^[1]

What are output tax and input tax?

Output tax is GST collected on taxable sales, while input tax is GST incurred on eligible business purchases and imports. The difference between output tax and input tax is the net GST payable to IRAS or refundable by IRAS.^[1]

A GST-registered business that collects S$9,000 of output tax and has S$4,000 of claimable input tax has a net GST position of S$5,000 payable to IRAS. A calculator can perform the subtraction, but it cannot determine whether every purchase satisfies the conditions for an input-tax claim.

Finance teams should therefore separate three tasks: calculating invoice GST, classifying transactions correctly and determining claim eligibility. Treating all GST appearing on supplier documents as automatically claimable can overstate input tax.

When must a Singapore business register for GST?

A business must generally register for GST when its taxable turnover is more than S$1 million under either the retrospective or prospective test.^[5]

The retrospective test applies when taxable turnover is more than S$1 million at the end of a calendar year. The prospective test applies when the business reasonably expects taxable turnover to be more than S$1 million in the next 12 months.^[5]

Taxable turnover includes standard-rated and zero-rated supplies but excludes exempt supplies, out-of-scope supplies and proceeds from selling capital assets.^[5] A business below the compulsory threshold may apply for voluntary registration after considering the associated obligations.^[5]

GST registration status determines whether a business may charge GST. A turnover calculator and an invoice GST calculator serve different purposes: the first assesses registration exposure, while the second calculates tax on a particular transaction.

How can businesses use a Singapore GST calculator safely?

Businesses should treat a GST calculator as an arithmetic tool rather than a substitute for transaction classification or tax advice.

Verify GST registration status. Confirm that the supplying entity is registered and entitled to charge GST.
Classify the supply. Identify whether the sale is standard-rated, zero-rated, exempt or out of scope.
Confirm the transaction date. Apply the rate and rules relevant to the transaction rather than relying only on the invoice preparation date.
Check the price basis. Establish whether the amount is GST-exclusive or GST-inclusive.
Add taxable fees first. Include compulsory service charges in the taxable base before applying GST.^[3]
Apply discounts correctly. Calculate GST on the adjusted consideration where the discount reduces the amount payable.
Use the correct formula. Multiply a net amount by 9% to calculate GST, or multiply a gross amount by 9/109 to extract it.^[2]
Round consistently. Round the total GST shown on the tax invoice to two decimal places.^[4]
Reconcile the records. Match invoice totals to accounting entries and investigate repeated rounding or classification differences.
Escalate unusual transactions. Obtain tax advice for cross-border supplies, mixed supplies, vouchers, reimbursements, reverse-charge transactions or uncertain exemptions.

What common GST calculation mistakes should finance teams avoid?

The most common GST errors arise from using the wrong price basis, calculation order or supply classification.

Mistake	Incorrect approach	Correct approach
Extracting GST from a gross price	Gross price × 9%	Gross price × 9/109
Adding GST to a net price	Net price + 9	Net price × 1.09
Ignoring compulsory service charge	Calculate GST before service charge	Add service charge, then calculate GST on the subtotal^[3]
Applying GST before a genuine price discount	Calculate GST on the original price	Reduce the consideration first, then calculate GST
Charging every transaction at 9%	Ignore the supply type	Classify the supply before calculating tax^[1]
Using a calculator to decide registration	Compare one invoice with the threshold	Assess taxable turnover under the retrospective and prospective tests^[5]
Rounding too early	Round intermediate calculations repeatedly	Calculate the invoice GST and round the total to the nearest cent^[4]
Treating GST collected as revenue	Include output tax in operating income	Record output tax separately as an amount accounted for to IRAS

A documented calculation policy helps sales, finance and operations teams apply the same order of calculations across quotations, invoices, credit notes and accounting entries.

How can E&H Corporate Services help with GST compliance?

E&H Corporate Services can support businesses with GST registration assessments, transaction reviews, accounting setup, GST computations and filing preparation.

A simple calculator answers “how much is 9% GST?” but does not determine whether a supply is taxable, whether input tax is claimable or whether a business has crossed the registration threshold.

Need help beyond the calculation? E&H Corporate Services can review your GST position, configure reliable accounting workflows and support ongoing tax compliance so that invoice calculations align with the underlying transaction treatment.

Frequently Asked Questions

The following answers cover the most common questions about using a GST calculator in Singapore.

What is 9% GST on S$100?

GST on a GST-exclusive amount of S$100 is S$9, producing a GST-inclusive total of S$109.

How do I add GST using a calculator?

Multiply the GST-exclusive amount by 1.09 to obtain the total, or multiply it by 0.09 to calculate the GST component alone.

How do I remove GST from a total?

Divide the GST-inclusive total by 1.09 to find the net price, or multiply the total by 9/109 to find the GST component.^[2]

Why can I not multiply a GST-inclusive price by 9%?

A GST-inclusive price already contains tax, so the GST component represents 9 parts of a 109-part total rather than 9% of the gross amount.

Is GST calculated before or after service charge?

GST is calculated after adding a compulsory service charge because the service charge forms part of the total price payable.^[3]

Is GST calculated before or after a discount?

GST is generally calculated after a genuine discount has reduced the consideration payable for the supply.

Should GST be rounded to two decimal places?

The total GST shown on a tax invoice may be rounded to the nearest whole cent, meaning two decimal places.^[4]

Does every Singapore business charge GST?

Only a GST-registered business may charge GST, and the correct treatment still depends on whether the particular supply is standard-rated, zero-rated, exempt or out of scope.

When is GST registration compulsory?

GST registration is generally compulsory when taxable turnover is more than S$1 million under the retrospective test or is reasonably expected to be more than S$1 million in the next 12 months under the prospective test.^[5]

Can a GST calculator determine whether input tax is claimable?

A GST calculator cannot determine claim eligibility because input-tax recovery depends on the nature of the purchase, supporting records and applicable GST rules.

What is the difference between a GST calculator and the IRAS GST Registration Calculator?

A GST calculator adds or extracts tax from a transaction, while the IRAS GST Registration Calculator helps a business assess whether its turnover creates a GST registration obligation.^[5]