If your business is registered for Goods and Services Tax (GST) in Singapore, filing your GST return on time and accurately is one of your most important compliance obligations. Yet it is also one of the most commonly mishandled — with errors in input tax claims, missed deadlines, and incorrect treatment of supply types being the most frequent causes of IRAS queries and penalties.

This guide provides a complete step-by-step workflow for filing your GST F5 return, a checklist of supporting documents you must retain, and the seven most common mistakes to avoid. It also covers the InvoiceNow requirement that came into force for new GST registrants from 1 April 2026. For a broader look at your compliance obligations, see our Singapore Company Compliance Calendar.

What Is a GST Return and When Must You File?

Every GST-registered business in Singapore is required to file a GST return — also known as the GST F5 — with the Inland Revenue Authority of Singapore (IRAS) after each accounting period. For most businesses, this is quarterly; some businesses elect to file monthly.

The filing deadline is one month after the end of each accounting period. So if your GST accounting period ends on 31 March, your return must be filed and any tax due settled by 30 April. Pursuant to Section 47 of the GST Act, every taxable person must submit a return for each accounting period and pay any tax due within one month of the end of that period.

Late filing attracts a penalty of S$200 per month, capped at S$10,000 per return. Late payment incurs a 5% penalty on the unpaid amount, with additional penalties for prolonged non-payment.

Step-by-Step GST F5 Return Workflow

Step 1: Reconcile Your Sales to the Sales Ledger

Begin by reconciling your total sales for the period to your accounting system. Identify and categorise every sale as either:

  • Standard-rated supply — 9% GST charged on the sale
  • Zero-rated supply — 0% GST (e.g., exports of goods, international services)
  • Exempt supply — no GST charged (e.g., financial services, residential property)
  • Out-of-scope supply — not subject to Singapore GST (e.g., third-country sales)

This categorisation directly affects the figures you enter in Boxes 1, 2, and 3 of the F5 form.

Step 2: Verify Tax Invoices for Input Tax Claims

For every purchase on which you intend to claim input tax, verify that you hold a valid tax invoice meeting IRAS requirements. A valid tax invoice must state: the sequential invoice number, date, supplier’s name and GST registration number, your name, description of the goods or services, the GST amount, and the total amount payable.

Input tax cannot be claimed on the basis of a proforma invoice, a statement, or a receipt that does not contain all required particulars. IRAS may disallow the claim if documentation is inadequate.

Step 3: Identify Disallowed Input Tax Claims

Not all input tax is claimable. The GST Act specifically disallows input tax on:

  • Motor cars (private passenger cars) and related expenses
  • Club memberships
  • Medical expenses for employees (unless compulsory under the Work Injury Compensation Act or employment contract)
  • Family benefits (e.g., recreational outings)

Entertainment expenses — such as business meals — are also partially restricted: the GST on entertainment is only 50% claimable where the recipient is a customer or client. Misclassifying these is one of the most common triggers for IRAS queries.

Step 4: Account for Import GST

If your business imports goods from overseas, check your IRAS-issued import permits (cleared through Singapore Customs). Import GST paid can be claimed as input tax — but only when supported by the original import permit, which must match your purchase records in terms of supplier, description, and value.

Step 5: Calculate Output Tax and Input Tax

Once your categorised supplies and verified input tax claims are in order:

  • Output tax = GST collected on your standard-rated sales and taxable imports
  • Input tax = GST paid on your business purchases (net of disallowed items)
  • Net GST payable / refundable = Output tax minus Input tax

If input tax exceeds output tax, you are in a refund position. IRAS typically processes refunds within 30 days for e-filed returns.

Step 6: Complete the GST F5 on myTax Portal

Log in to the IRAS myTax Portal using your CorpPass credentials. The F5 form has eight boxes:

  • Box 1: Total value of standard-rated supplies
  • Box 2: Total value of zero-rated supplies
  • Box 3: Total value of exempt supplies
  • Box 4: Total value of all supplies (Box 1 + 2 + 3)
  • Box 5: Total value of taxable purchases
  • Box 6: Output tax due
  • Box 7: Input tax and refunds claimed
  • Box 8: Net GST payable or refundable (Box 6 minus Box 7)

Double-check every figure before submission. Once submitted, corrections require an amendment return (GST F7) or a written request to IRAS.

Step 7: Archive Supporting Documents (Five-Year Retention)

Under the GST Act, you are required to retain all GST records — including tax invoices, credit notes, import permits, expense claims, and accounting ledgers — for a minimum of five years from the end of the accounting period to which they relate. This applies even after you deregister for GST. See also our guide to accounting record retention in Singapore.

The InvoiceNow Requirement: What Changed from 1 April 2026

A significant change took effect on 1 April 2026: all new voluntary GST registrants — regardless of business structure or date of incorporation — are now required to transmit invoice data to IRAS via the InvoiceNow network at the time of filing their GST return.

InvoiceNow is Singapore’s national e-invoicing network, built on the international Peppol framework. It allows invoice data to flow directly from your accounting system to IRAS in real time, reducing manual reconciliation errors and speeding up GST audits. IRAS has also confirmed that the requirement will be extended to all existing GST-registered businesses between 1 April 2028 and 1 April 2031 on a phased basis.

Full details of the phased implementation are available on the IRAS GST InvoiceNow requirement page.

Seven Common GST Mistakes That Trigger IRAS Queries

  1. Claiming input tax on disallowed expenses — particularly entertainment, private car expenses, and club memberships.
  2. Errors in partial exemption apportionment — if your business makes both taxable and exempt supplies, only input tax attributable to taxable supplies is claimable. The apportionment formula must be applied correctly each period.
  3. Missing import GST claims — failing to include GST paid on imported goods as claimable input tax when supported by import permits.
  4. Incorrect zero-rating of supplies — zero-rating an export without holding the required export evidence (e.g., export permit, bill of lading, airway bill).
  5. Arithmetic errors — simple calculation mistakes between your accounting records and the F5 form, particularly in Box 4 and Box 8.
  6. Late filing and late payment — missing the one-month deadline triggers automatic penalties. Set calendar reminders for every accounting period end date.
  7. Claiming input tax on invoices not in your company’s name — input tax can only be claimed by the business named on the tax invoice.

GST Refunds: Criteria and Timeline

If you are in a net refund position (input tax exceeds output tax), IRAS will process your refund after reviewing the return. The typical timeline is 30 days for e-filed returns. IRAS may request supporting documents before releasing a refund, particularly for large refund claims or where an audit flag is triggered.

To expedite refunds, ensure your bank account details are up to date on the myTax Portal under “Update GIRO/Bank Account.”

GST Return Filing Checklist

Pre-Filing

  • Sales reconciled to the sales ledger by supply type (standard-rated, zero-rated, exempt, out-of-scope)
  • All tax invoices for input tax claims verified for required particulars
  • Disallowed input tax items (private cars, entertainment at 50%, medical benefits) excluded
  • Import GST matched to corresponding import permits
  • Credit notes issued and received accounted for and adjusted

At Filing

  • All eight boxes on the F5 accurately completed and cross-checked
  • InvoiceNow data transmitted (if required under the phased mandate)
  • Return submitted by the due date (one month after period end)
  • Payment arranged via GIRO deduction or manual payment on myTax Portal

Post-Filing

  • Filing confirmation receipt retained
  • All supporting documents archived for a minimum of five years
  • Any discrepancies or overpayments flagged to IRAS in writing promptly
  • Refund bank account details updated on myTax Portal if applicable

For related compliance obligations, see our guides on XBRL filing with ACRA and withholding tax in Singapore.

How Raffles Corporate Services Can Help

Managing GST compliance in-house can be time-consuming, particularly for businesses with a mix of standard-rated, zero-rated, and exempt supplies. Raffles Corporate Services provides professional GST return preparation and filing services, helping your business stay compliant with IRAS requirements while avoiding the most common — and costly — errors.

For the latest Singapore business news and regulatory updates, there are useful resources for directors and business owners staying on top of IRAS changes.

Beyond tax compliance, sound financial planning and investment decisions are equally important for business owners managing their overall financial health.

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