If your company is registered for Goods and Services Tax (GST) in Singapore, filing your GST return accurately and on time is a non-negotiable compliance obligation. The GST F5 return — submitted quarterly for most businesses — is how you report your output tax (GST collected on sales) and input tax (GST paid on purchases) to the Inland Revenue Authority of Singapore (IRAS). Get it wrong, and you face penalties, IRAS audits, and cash flow disruptions.

This guide breaks down the full GST return filing workflow, the supporting documents you must have in order, and the seven most common mistakes that trigger IRAS scrutiny — complete with a pre-filing and post-filing checklist.

What Is the GST F5 Return?

The GST F5 is the standard periodic return filed by GST-registered businesses in Singapore. Most businesses file quarterly — on a Jan–Mar, Apr–Jun, Jul–Sep, or Oct–Dec basis — with the return due one month after the end of each accounting period. A company with a March quarter-end must therefore file by 30 April.

Businesses may elect to file monthly if they regularly receive GST refunds (for example, exporters claiming back input tax on goods sold at zero-rate). Monthly filing requires IRAS approval.

The F5 return is filed electronically via the IRAS myTax Portal, using your company’s CorpPass. Late filing attracts a penalty of S$200 per month outstanding, up to a cap of S$10,000 per return — so late submission adds up fast.

Step-by-Step GST Return Filing Workflow

Step 1: Reconcile Your Sales Ledger

Begin with your sales records. Reconcile all sales invoices for the quarter against your accounting system’s sales ledger. Categorise each supply as standard-rated (9% GST), zero-rated (0% GST, typically exports and certain international services), or exempt (no GST, such as most financial services and residential property rentals).

Your total taxable supplies — standard-rated plus zero-rated — go into Box 1 of the F5. Exempt supplies go into Box 3. The GST collected on standard-rated supplies is your output tax (Box 6).

Step 2: Verify Tax Invoices for Input Tax Claims

For every GST claim on purchases and expenses, confirm you hold a valid tax invoice from a GST-registered supplier. Under the Goods and Services Tax Act 1993, a valid tax invoice must show the invoice number, date, supplier’s name and GST registration number, description of goods or services, quantity supplied, total amount payable excluding GST, and the GST charged. Receipts, quotes, and proforma invoices do not qualify as tax invoices — they cannot support an input tax claim.

Step 3: Identify Disallowed Input Tax

Not every GST you pay is claimable. Singapore’s GST rules block input tax claims on certain expense categories regardless of whether you hold a valid tax invoice. Disallowed items include:

  • Medical expenses for employees (unless the company is in the business of providing medical treatment)
  • Club membership fees
  • Family benefits provided to employees’ family members
  • Entertainment expenses (unless you are in the business of providing entertainment)
  • Costs relating to motor cars (registration number beginning with S, unless the car is used exclusively for business purposes such as for hire or driving instruction)
  • Transactions where the business is the recipient of benefits under a GST group registration but the expense relates to exempt supplies

Claiming input tax on any of these categories is one of the most common triggers for IRAS audit action.

Step 4: Apportion Input Tax if You Make Both Taxable and Exempt Supplies

If your company makes both taxable supplies (standard-rated and zero-rated) and exempt supplies (for example, a firm that earns both consultancy fees and rental income from residential properties), you cannot claim the full input tax on overhead expenses. You must apportion the input tax using an IRAS-approved method — most commonly the Standard Input Tax Recovery (STR) method, which calculates the ratio of taxable supplies to total supplies for the period.

Failure to apportion where required is a material error and a frequent source of IRAS assessments.

Step 5: Calculate Net GST Payable or Refundable

Your net GST position is:

Output Tax (Box 6) minus Claimable Input Tax (Box 7) = Net GST Payable or Refundable (Box 13/14)

If output tax exceeds input tax, you owe GST to IRAS. If input tax exceeds output tax (common for exporters), IRAS owes you a refund. Most businesses are in a net payable position.

Step 6: Complete and Submit the F5 on myTax Portal

Log in to myTax Portal using your company’s CorpPass. Under GST, select “File GST Return (F5)”. The portal will pre-populate some fields if you have configured InvoiceNow (see below). Fill in the boxes accurately:

  • Box 1: Total value of standard-rated supplies (excluding GST)
  • Box 2: Total value of zero-rated supplies
  • Box 3: Total value of exempt supplies
  • Box 4: Total value of all supplies (sum of Boxes 1, 2, 3)
  • Box 5: Total value of taxable purchases (excluding GST)
  • Box 6: Output tax (9% of Box 1)
  • Box 7: Input tax claimable
  • Box 8: Input tax on capital goods where capital goods adjustment applies
  • Box 9: Bad debt relief claimed
  • Box 10: Pre-registration input tax claimed
  • Box 11: Input tax adjustment for GST incurred on goods that are not wholly for business use
  • Box 12: Net tax (Box 6 minus Boxes 7 to 11)
  • Box 13: If Box 12 is positive, this is the GST payable to IRAS
  • Box 14: If Box 12 is negative, this is the GST refundable to you

Double-check every figure before submitting. Once submitted, errors require a voluntary disclosure to IRAS or, if IRAS discovers them first, will attract penalties.

Step 7: Archive Supporting Documents for Five Years

Under Section 46 of the GST Act, all records supporting your GST returns must be kept for five years from the end of the relevant accounting period. This includes sales invoices, purchase invoices and receipts, import permits, credit and debit notes, bank statements reconciling your GST payments, and documentation of apportionment calculations.

IRAS audits can cover any period within the five-year window. Missing records will result in input tax disallowance and potential penalties.

The InvoiceNow Update: What Changes for Your Filing Workflow

Since 1 April 2026, all new voluntary GST registrants are required to transmit invoice data to IRAS via the InvoiceNow e-invoicing network at the point of billing — not just at the time of filing the F5 return. This is a significant shift: invoice data must flow to IRAS in near-real-time through a Peppol-compliant accounting system, rather than being aggregated and submitted in a return at period-end.

The rollout timeline for existing GST-registered businesses is:

  • 1 April 2028: New compulsory registrants and existing businesses with annual taxable supplies of S$200,000 or less
  • 1 April 2029: Existing businesses with annual taxable supplies up to S$1,000,000
  • 1 April 2030: Existing businesses with annual taxable supplies up to S$4,000,000
  • 1 April 2031: All remaining GST-registered businesses

For businesses already subject to InvoiceNow, the F5 return becomes more of a confirmation exercise — IRAS will have much of your invoice data before you file. Popular accounting packages including Xero, QuickBooks, and Sage have already built InvoiceNow compliance into their Singapore editions.

GST Refund Claims: What to Expect

If your F5 shows a refund due (Box 14 is populated), IRAS will review your refund claim before releasing funds. The standard processing time is about a month for straightforward returns. IRAS may ask for supporting documents, particularly for first-time refund claims or unusually large amounts. You can check refund status on myTax Portal.

To minimise delays: ensure your bank details on GIRO are current, file on time, and have all supporting documentation ready before submission. Do not amend a return expecting to claim a refund — IRAS tracks submission patterns and amendments trigger reviews.

Seven Common GST Mistakes That Trigger IRAS Queries

Mistake 1: Claiming Input Tax on Disallowed Expenses

As noted above, GST on entertainment, private motor cars, club memberships, and family benefits of employees cannot be claimed. This is the single most common mistake uncovered in IRAS GST audits.

Mistake 2: Entering GST-Inclusive Amounts Instead of Exclusive Amounts

Boxes 1–5 in the F5 require the value of supplies and purchases excluding GST. A common error is entering the GST-inclusive total, which overstates output tax and distorts the return. Always strip out the GST component before entering figures.

Mistake 3: Failing to Apportion Input Tax for Partially Exempt Businesses

If you make any exempt supplies at all — rental of residential property, provision of certain financial services — overhead input tax must be apportioned. Many businesses either do not know this rule or forget to apply it once they begin making exempt supplies.

Mistake 4: Missing Import GST

GST is payable at the time of importation and can be claimed as input tax if you hold the import permit (the Customs IN permit). If import permits are filed centrally by a freight forwarder and not shared with your finance team, the input tax claim is easily missed — as is the obligation to account for import GST if you used a suspended scheme improperly.

Mistake 5: Incorrect Treatment of Zero-Rated Supplies

Zero-rating applies to exports of goods and certain international services — but the conditions are strict. An export must be supported by export documentation (export permit, bill of lading or airway bill, commercial invoice). International services must satisfy the conditions in the Fourth Schedule of the GST Act. If evidence is insufficient, IRAS will reclassify the supply as standard-rated and assess 9% GST on the full value.

Mistake 6: Late Filing

The due date is one month after the accounting period ends. File by the deadline even if you expect to make corrections later. A S$200 penalty applies immediately for each day the return is outstanding, compounding monthly up to a S$10,000 cap per return — plus IRAS can seek a court order for payment.

Mistake 7: Inadequate Record Retention

IRAS auditors routinely request source documents — original tax invoices, import permits, and bank statements — to verify F5 figures. If your company cannot produce records for a period under audit because files were discarded before the five-year window elapsed, IRAS will disallow the relevant input tax claims in full.

GST Return Filing Checklist

Pre-Filing Checklist

  • ☐ All sales invoices reconciled against sales ledger
  • ☐ Supplies categorised as standard-rated, zero-rated, and exempt
  • ☐ Valid tax invoices obtained for all input tax claims
  • ☐ Disallowed expense categories identified and excluded
  • ☐ Apportionment calculation completed if any exempt supplies made
  • ☐ Import permits obtained from freight forwarder for the period
  • ☐ Export documentation verified for all zero-rated sales
  • ☐ CorpPass credentials available for myTax Portal login

At-Filing Checklist

  • ☐ All F5 boxes completed using values excluding GST
  • ☐ Box 6 (output tax) cross-checked against 9% of Box 1
  • ☐ Box 7 (input tax) confirmed against claimable invoice amounts only
  • ☐ Net tax position (Box 13 or Box 14) verified before submission
  • ☐ Submission confirmed before the filing due date
  • ☐ Acknowledgement receipt saved from myTax Portal

Post-Filing Archiving Obligations

  • ☐ All sales invoices filed and stored for five years
  • ☐ All purchase invoices and receipts stored for five years
  • ☐ Import permits and export documentation stored for five years
  • ☐ Credit and debit notes stored for five years
  • ☐ Bank statements covering the period stored for five years
  • ☐ Apportionment calculation worksheets stored for five years

How GST Compliance Fits Into Your Annual Compliance Calendar

GST filing is one of several recurring obligations facing Singapore companies. The full picture — corporate tax, ACRA annual returns, CPF, and payroll — is set out in our Singapore Company Compliance Calendar 2026. You may also find our guides to GST Registration in Singapore 2026 and Singapore Tax Penalties useful background reading.

For directors managing broader compliance requirements for Singapore companies, it is worth noting that GST compliance status forms part of ACRA’s assessment when reviewing striking-off applications and annual lodgements. A company with outstanding GST returns cannot be struck off.

Sound financial management and investment decisions for business owners start with getting the fundamentals right — and GST compliance is one of those fundamentals. For up-to-date coverage of Singapore tax changes, Singapore financial news is a useful resource for business owners and directors.

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