If your Singapore company is registered for Goods and Services Tax (GST), filing your GST return accurately and on time is one of the most important compliance obligations you face. Yet it is also one of the areas where mistakes are most common — and most costly. The Inland Revenue Authority of Singapore (IRAS) audits approximately 3,000 GST-registered businesses each year, recovering an average of more than S$18,000 in GST and penalties per business audited.

This guide walks you through the complete GST return filing workflow for Singapore companies in 2026, covering the step-by-step process, supporting documents you must retain, the InvoiceNow update that took effect from 1 April 2026, and a checklist of the seven most common mistakes that trigger IRAS scrutiny.

What Is a GST Return and When Must You File?

A GST return — known as the F5 Return — is the periodic declaration you submit to IRAS reporting your output tax (GST collected from customers) and input tax (GST paid on business purchases), with the net amount either payable to IRAS or refundable to your company.

Key filing rules under the Goods and Services Tax Act 1993:

  • Quarterly filing is the default for most GST-registered businesses. Each return covers a 3-month accounting period.
  • Monthly filing is available by election — useful if your business regularly receives GST refunds (e.g. exporters with predominantly zero-rated supplies).
  • Deadline: returns must be submitted and payment made within one month after the end of each accounting period. For example, if your accounting period ends 31 March, your GST F5 is due by 30 April.
  • Nil returns: even if you had no transactions during a period, you must still file a nil return (enter “0” in all boxes). Failure to do so attracts late filing penalties.

Step-by-Step GST Return Filing Workflow

Step 1 — Reconcile Your Sales Ledger to Sales Invoices

Before you open the IRAS myTax Portal, reconcile your sales invoices against your accounting system’s general ledger for the period. Every taxable supply must be captured. Check that all invoices are correctly coded — standard-rated (SR, 9%), zero-rated (ZR, 0%), or exempt — and that no invoices have been missed or double-counted.

Step 2 — Verify Tax Invoices for Input Tax Claims

For every GST expense you intend to claim as input tax, confirm that you hold a valid tax invoice from a GST-registered supplier. Under Section 38 of the GST Act, a valid tax invoice must state:

  • The supplier’s name and GST registration number
  • The date of supply
  • A description of the goods or services supplied
  • The total payable excluding GST, the GST amount, and the total payable including GST

A receipt, a delivery order, or a proforma invoice does not qualify. Simplified tax invoices (for supplies of S$1,000 or less including GST) require fewer details but must still show the supplier’s GST number.

Step 3 — Identify Your Supply Categories

Classify every supply in the period into the correct category for Boxes 1–4 of the F5 form:

  • Box 1: Total value of standard-rated supplies (9% GST)
  • Box 2: Total value of zero-rated supplies (exports, international services)
  • Box 3: Total value of exempt supplies (financial services, residential property)
  • Box 4: Total value of out-of-scope supplies (private transactions, third-country transactions)

Step 4 — Calculate Output Tax and Input Tax

Output tax (Box 6) is 9% of your Box 1 figure. Input tax (Box 7) is the total GST paid on business purchases that are claimable. If your business makes both taxable and exempt supplies, you may need to apportion your input tax claim — only the portion attributable to taxable supplies is recoverable.

Step 5 — Compute Net GST Payable or Claimable

Box 8 = Box 6 minus Box 7. If positive, this is GST payable to IRAS. If negative, you have a net input tax credit and can claim a GST refund.

Step 6 — File via myTax Portal

Log in to myTax Portal using your company’s CorpPass credentials. The person filing must be assigned the “GST (Filing and Applications)” e-service role in CorpPass. Navigate to GST → File GST Return (F5/F7/F8), select the correct accounting period, enter your figures in all 15 boxes, review, and submit. All figures must be in Singapore dollars.

Step 7 — Archive Supporting Documents

Under the GST Act, you must retain all GST records — including tax invoices, receipts, import permits, and bank statements — for a minimum of five years from the end of the relevant accounting period. IRAS can conduct audits for any period within the past five years, so systematic document retention is not optional.

The InvoiceNow Update: What Changed From 1 April 2026

From 1 April 2026, all new voluntary GST registrants — regardless of when their company was incorporated — must adopt an IRAS-approved InvoiceNow e-invoicing solution. InvoiceNow transmits structured invoice data directly to IRAS through the Peppol network, enabling near-real-time tax administration.

This affects your GST return filing workflow in two important ways:

  • Your invoicing software must be InvoiceNow-compliant. Check the IRAS website for the list of approved solutions.
  • Invoice data is transmitted to IRAS electronically, which means IRAS may cross-reference your GST return figures against the data already received — making accuracy even more critical.

Businesses that were voluntarily GST-registered before 1 November 2025 are not immediately required to adopt InvoiceNow, but IRAS has signalled that compulsory adoption will be extended progressively. You can read more about the GST InvoiceNow requirement on our site.

Seven Common GST Return Mistakes (and How to Avoid Them)

Mistake 1 — Claiming Input Tax on Disallowed Expenses

Regulations 26 and 27 of the GST (General) Regulations specifically disallow input tax on certain categories of expenses, no matter how legitimate the business purpose:

  • Benefits provided to family members or relatives of staff
  • Running costs and purchase of private cars (S-plated vehicles)
  • Club membership fees
  • Medical expenses (except those required under the Work Injury Compensation Act or a collective agreement)

Mistake 2 — Missing or Invalid Tax Invoices

Claims without a valid supporting tax invoice will be disallowed on audit. Common sub-errors: the invoice is addressed to the wrong entity, the supplier’s GST number is missing, or a proforma invoice has been mistakenly used. Check every invoice before filing.

Mistake 3 — Errors in Apportionment for Partially Exempt Businesses

If your company makes both taxable and exempt supplies (for example, a financial services firm that also provides consultancy), you must apportion input tax claims. Only the proportion attributable to taxable supplies is recoverable. Using an incorrect apportionment method — or failing to apportion at all — is one of the most common audit triggers.

Mistake 4 — Missing Import GST

GST is payable on goods imported into Singapore. If your business imports goods, import GST is typically paid at the point of customs clearance. You may then claim this as input tax if you hold the relevant import permit (in-payment permit) as the named importer. Failing to capture import GST in your return — either missing the liability or missing the claim — is a common error.

Mistake 5 — Incorrect Treatment of Zero-Rated Exports

Exports of goods and certain international services are zero-rated (0% GST), not exempt. The distinction matters because you can still claim input tax credits on costs related to zero-rated supplies, but not on costs related to exempt supplies. Miscoding an export as exempt will cause you to under-claim input tax.

Mistake 6 — Late Filing

Filing after the deadline attracts a late filing penalty of S$200 per return (up to a maximum of S$10,000), and late payment of GST owed attracts a 5% late payment penalty plus interest. Set calendar reminders one month in advance of each GST filing deadline — or engage an accounting firm to manage this on your behalf. See our Singapore Company Compliance Calendar 2026 for all key dates.

Mistake 7 — Arithmetic and Data Entry Errors

Manual entry in the myTax Portal is prone to transposition errors and rounding mistakes. Always reconcile the figures on your F5 submission back to your accounting system totals before clicking Submit. A difference of even S$1 can prompt an IRAS query.

GST Return Filing Checklist

Pre-filing checklist (do this before you open myTax Portal):

  • ☐ All sales invoices issued in the period are captured and correctly coded (SR/ZR/ES/OS)
  • ☐ All purchase invoices with input tax claims have been verified as valid tax invoices
  • ☐ Disallowed expenses (cars, club memberships, family benefits, medical) have been excluded
  • ☐ Import permits checked and import GST recorded
  • ☐ Apportionment calculation done (if applicable)
  • ☐ Reconciliation of GST workings to general ledger completed
  • ☐ CorpPass user has GST Filing e-service role assigned

At-filing checklist:

  • ☐ Correct accounting period selected on myTax Portal
  • ☐ All 15 boxes reviewed and cross-checked
  • ☐ Figures in Singapore dollars
  • ☐ Acknowledgement page saved after submission
  • ☐ Payment scheduled (if GST is payable) by the due date

Post-filing archiving:

  • ☐ All tax invoices, import permits, credit notes, and expense receipts archived (5-year retention)
  • ☐ Accounting system updated to reflect filed return
  • ☐ Next period’s accounting start date confirmed

GST Refund Claims

If your F5 return shows net input tax credits — common for exporters and businesses with significant capital expenditure — you can claim a GST refund. IRAS processes refund claims within 10 business days of receiving a complete return (certain complex cases may take longer). Refunds are paid by GIRO directly to your designated bank account. Ensure your GIRO banking details are updated in myTax Portal to avoid delays.

Correcting Errors: The GST F7 Return

If you discover an error in a previously submitted GST return, you must file a GST F7 (Disclosure of Errors) return. If you voluntarily disclose within one year of the original filing deadline and meet the qualifying conditions under IRAS’s Voluntary Disclosure Programme (VDP), no late payment penalty is imposed on the additional GST payable. Early, voluntary correction is always preferable to waiting for an IRAS audit.

How Singapore Secretary Services Can Help

GST return filing is a monthly or quarterly obligation that requires meticulous record-keeping and up-to-date knowledge of IRAS rules. At Raffles Corporate Services, our accounting and GST compliance team handles GST registration, return preparation, submission, and IRAS correspondence on behalf of Singapore companies of all sizes. We also help with the transition to InvoiceNow-compliant e-invoicing. For a fuller picture of your annual compliance obligations, see our guide to the Singapore Company Compliance Calendar 2026.

For sound financial management and business planning, staying on top of GST compliance is as important as any growth strategy. For the latest Singapore business news and regulatory updates, there are useful resources for directors and business owners. If you need legal advice on your GST compliance obligations, we can point you in the right direction.

To speak with the team at Raffles Corporate Services, you can email [email protected] or call, SMS, or WhatsApp +65 8501 7133. We are happy to assist with any queries.

— The Editorial Team, Raffles Corporate Services