Input tax vs output tax — what's the difference?

Output tax is the GST you charge customers on your sales. Input tax is the GST you pay suppliers on your business purchases. The difference — output tax minus input tax — is the net GST you owe IRAS (or that IRAS refunds to you) each quarter, declared on your GST F5.

This is the core mechanic of value-added tax: businesses act as the collectors of GST on the government's behalf, paying only the value they add.

A worked example

You're a GST-registered Singapore consultancy.

| | Amount | GST (9%) | |---|---|---| | Sales (output) — invoice to client | S$10,000 | S$900 (output tax) | | Purchases (input) — laptop + cloud hosting | S$2,000 | S$180 (input tax) | | Net GST owed to IRAS | | S$720 |

That S$720 is the figure that ends up on your GST F5 for the quarter. If, in some quarter, your input tax exceeds your output tax (e.g. a heavy investment month), IRAS refunds the difference.

Conditions for claiming input tax

You can't just claim every GST cost. IRAS lists strict conditions:

You must be GST-registered. If you're not, you can't claim input tax.
The purchase is for business purposes. Goods or services used for genuine business activity. Excludes private/personal use, charity, etc.
The input is attributable to taxable supplies. Most ordinary sales qualify (standard-rated or zero-rated). Input tax on purchases used to make exempt supplies generally can't be claimed.
You hold a valid tax invoice from your supplier (or import permit, for imports).
You claim in the right accounting period — the period corresponding to the invoice/import permit date.

Some categories are blocked from input-tax claims entirely (e.g. private motor cars and their running expenses, club subscriptions, family benefits).

Why it matters operationally

Getting input vs output tax right is the bookkeeping work that makes GST filing accurate. In practice, errors come from:

Tax codes set wrong on a supplier or product (e.g. 0% applied to a standard-rated import)
GST claimed on personal expenses run through the business
Missing tax invoices when claiming input tax
Claiming input tax in the wrong period (e.g. on payment date rather than invoice date)

The GST InvoiceNow Requirement helps with the first and third — invoice data goes straight to IRAS in structured form, so coding errors and missing tax invoices are caught earlier.

GST (Goods and Services Tax) — GST is Singapore's broad-based consumption tax — currently 9% — charged on most goods, services and imports.
GST F5 — GST F5 is the quarterly GST return every GST-registered business in Singapore files with IRAS.
Tax invoice (Singapore) — A tax invoice is the document a GST-registered Singapore business issues so its GST-registered customer can claim input tax.
GST registration threshold — Singapore businesses must register for GST when taxable turnover exceeds S$1 million — either retrospectively or on a forecast (prospective) basis.

Sources

Last reviewed 29 May 2026. Verify any thresholds or dates against the official source above before relying on them.