An export worth S$500,000 can be treated as a local sale if the business cannot provide the required shipping documents. IRAS may then treat the price as including GST, meaning about S$41,300 of it is GST that the exporter must pay, even if the overseas customer never paid GST.
Many errors described in IRAS audit guidance come from paperwork or incorrect tax codes, rather than deliberate evasion. These mistakes can still be costly. In FY2024/25, IRAS completed more than 2,800 GST audits and recovered S$205 million in tax and penalties, averaging about S$70,000 per audit.
This guide explains the GST mistakes IRAS commonly identifies, as well as what each one can cost and how to correct them before penalties increase.
| Quick Answer
Common GST errors include claiming input tax without the required documents, applying 0% GST to exports without proof, and filing returns late. Some errors can be corrected in your next GST F5; others require a GST F7. |
Key Takeaways
- Input tax claims need a valid tax invoice or import permit. GST on motor cars, club fees, and most staff medical costs generally cannot be claimed.
- Keep the required export documents within 60 days to support 0% GST treatment. Without them, IRAS may treat the sale as GST-inclusive.
- For sales above S$1,000 to GST-registered customers, issue a full tax invoice within 30 days.
- Small errors can be corrected in your next GST F5 only if they meet both IRAS tests, including the often-overlooked 5% test based on the value of supplies.
- Errors disclosed within IRAS’s one-year grace period carry no penalty.
- Voluntary GST registration lasts at least two years. New voluntary registrants from 1 April 2026 must also use InvoiceNow.
Singapore GST Rules at a Glance
Singapore charges GST at 9%. Every GST-registered business must file a GST F5 return for each accounting period, usually every quarter. Most mistakes covered in this guide involve one of the rules below.
| Rule | Current requirement | Where businesses slip |
| GST rate | 9% on standard-rated supplies, since 1 January 2024 | Old 7% or 8% rates left in invoice templates or accounting software |
| Compulsory registration | Taxable supplies above S$1 million in a calendar year, or expected to exceed S$1 million in the next 12 months | Checking only past sales and missing a large contract just signed |
| Applying to register | Within 30 days of becoming liable | Waiting until the revenue has come in |
| Tax invoices | Issued within 30 days of the supply; simplified invoices allowed up to S$1,000 including GST | Using simplified invoices for larger B2B sales |
| Filing and payment | One month after the end of each accounting period, nil returns included | Skipping a return in a quiet quarter |
| Correcting errors | Small errors in the next GST F5; others through a GST F7 (see the step-by-step section) | Making an adjustment in the next return when a GST F7 is required |
| Refunds and records | Overpaid GST claimable within 5 years; records kept for at least 5 years | Missing invoices and export papers when IRAS asks |
Registration Mistakes
Registration mistakes can quickly pile up and become expensive. A business that should have registered but continues trading without doing so may owe GST on past sales that it can no longer collect from customers.
Registering late when GST registration is compulsory
GST registration is compulsory if either of two tests is met. The first looks at past sales: taxable supplies exceeded S$1 million during a calendar year. The second looks ahead: if you can reasonably expect taxable supplies to exceed S$1 million in the next 12 months, you may already need to register, for example after winning a large contract. This second test is easy to miss because the expected sales may not yet appear in your accounts.
You must apply within 30 days of becoming liable to register. For forecasts made on or after 1 July 2025, registration takes effect two months after the date you make the forecast, giving you time to update invoices and prices.
If you miss the deadline, IRAS may backdate your registration. You would then owe GST on sales made from the effective registration date, even if you had not charged customers GST. IRAS may impose a penalty equal to 10% of that GST and a fine of up to S$10,000. Apply as soon as you realise the mistake and disclose the delay. IRAS may waive the fine and penalties and allow you to pay the backdated GST in instalments.
Registering voluntarily without checking the costs and benefits
Voluntary GST registration can help some businesses but cost others money. The main factor is who your customers are.
| Voluntary registration usually pays off when… | Think twice when… |
| Most of your customers are GST-registered and can claim back the 9% you charge | Most customers are consumers who cannot claim GST, so you either raise prices or absorb the 9% |
| Most of your suppliers charge GST, which you can then recover | Most of your costs carry no GST, such as salaries |
| You export goods or international services that qualify for 0% GST | Your sales are mostly exempt from GST, leaving little input tax to recover |
| Your sales are close to S$1 million and still growing | Nobody on the team has time for quarterly filing and InvoiceNow |
Registration can help with purchases. For example, if you buy S$1,000 of supplies from a GST-registered vendor, you can usually claim back S$90 in GST. The effect on sales can be less favourable. If most of your customers are consumers, you may need to raise prices by 9% or absorb the GST yourself. Consumers cannot claim that GST back. For a consumer-facing business with few GST-bearing costs, voluntary registration may offer little benefit.
Voluntary registration also creates ongoing obligations and a minimum two-year commitment. Before applying, a director or your GST preparer must pass IRAS’s “Overview of GST” e-learning course. You must use GIRO, stay registered for at least two years and, for applications made from 1 April 2026, send invoice data through InvoiceNow.
Input Tax Claim Mistakes
Input tax is the GST a business pays on its purchases. It reduces the GST the business owes on sales, known as output tax. If input tax is higher than output tax, IRAS may refund the difference. IRAS also audits businesses that make small refund claims. To claim input tax, you need a valid tax invoice addressed to your business or an import permit for imported goods, and the expense must be one that IRAS allows.
Can I claim the GST? A quick reference
| Expense | Claimable? | What to know |
| Office rent, utilities, professional fees | Yes | The tax invoice must be addressed to the business |
| Staff medical expenses and medical insurance | Usually no | GST may be claimed only in limited cases, such as when the expense is required under the Work Injury Compensation Act or a collective agreement |
| Club subscription and transfer fees | No | Applies to sports and recreation clubs, even when used to entertain clients |
| Motor cars | No | Includes buying, hiring and running costs for motor cars; goods vehicles such as vans are treated differently |
| Benefits for employees’ family members | No | GST on costs for employees’ family members is not claimable; a company family day attended by staff relatives is a common example |
| Household bills for a home-based business | No | IRAS treats household bills as personal expenses, even when you work from home |
| Purchases made before registration | Sometimes | You may claim GST on goods still held when registration starts and on services bought in the six months before registration. Include the claim in your first GST return. |
Income tax and GST follow different rules. For example, staff medical costs may be deductible for income tax, but the GST paid on them is generally not claimable as input tax. Our guide to allowable business expenses covers the income tax side.
Claiming from the wrong document
A quotation, pro forma invoice, or statement of account is not a valid tax invoice, so it does not support an input tax claim. You also cannot claim GST using an invoice addressed to a director personally. If you have not received the correct tax invoice when preparing your return, leave the claim out until you receive it.
Claiming GST you were wrongly charged
You cannot claim GST charged by a supplier that is not GST-registered, even if the invoice looks official. Check the supplier using IRAS’s GST Registered Business Search. When buying digital services or low-value goods from overseas sellers, provide your GST registration number at checkout so the seller does not charge GST. If the seller charges GST anyway, you still cannot claim it as input tax.
Claiming private expenses
Running a business from home does not automatically make household bills business expenses. In one published case, IRAS disallowed a company’s GST claims for utilities, phone charges, and maintenance at a residential property because the expenses were mainly personal.
Claiming in the wrong period, or twice
Claim input tax in the accounting period determined by the date on the tax invoice or import permit. Duplicate claims can happen when a supplier sends the same invoice more than once. A duplicate-invoice-number check in your accounting software, or a manual check during review, can help catch them.
Leaving a supplier bill unpaid for 12 months
You may claim input tax before paying the supplier, but there is a time limit. If the bill remains unpaid 12 months after its due date, you must reverse the input tax by reducing Box 7 in your GST return. If you pay the bill later, you can claim the input tax again within five years from the end of the accounting period in which you first claimed it.
Claiming GST refunds when the company is dormant
Input tax claims must relate to taxable business supplies. A company that has stopped trading generally cannot show that its expenses relate to such supplies. IRAS lists claims by dormant companies among the common errors found in its refund audits. These audits may include visits to business premises and interviews with key staff.
Tax Invoice Mistakes
A tax invoice records your sale and gives your GST-registered customer the document needed to claim input tax. An error can affect both your business and your customer.
| Document | Use it when | It must show |
| Full tax invoice | You sell to a GST-registered customer and the total, including GST, is above S$1,000 | The words “Tax Invoice”; invoice number and date; your name, address and GST registration number; the customer’s name and address; a description; the amount before GST; the GST rate and amount; the total including GST |
| Simplified tax invoice | The total, including GST, is S$1,000 or less | Your name, address and GST registration number; invoice number and date; a description; the total including GST; the words “Price payable includes GST” |
| Receipt | You sell to a customer who is not GST-registered | Your GST registration number, the date, and the amount paid |
The following mistakes may prevent a customer from claiming input tax or put your business in breach of GST rules:
- A missing GST registration number, or no “Tax Invoice” heading.
- A simplified tax invoice issued for a sale above S$1,000.
- An invoice issued more than 30 days after the supply.
- For an invoice issued in a foreign currency, show the amount before GST, the GST amount, and the total including GST in Singapore dollars as well. Convert these amounts using an IRAS-approved exchange rate (for example, a rate from a local bank) that is updated at least once every three months.
- GST charged before your registration takes effect. An unregistered business cannot charge GST. Doing so can lead to a penalty of three times the amount collected, a fine of up to S$10,000, imprisonment for up to three years, or both.
Invoice data is also being sent directly to IRAS in phases under the GST InvoiceNow Requirement. The government has said the data will help strengthen IRAS’s risk analysis. Our InvoiceNow guide explains how to prepare.
| From | Who must comply |
| 1 April 2026 | All new voluntary GST registrants |
| 1 April 2028 | New compulsory registrants, and existing businesses with annual supplies up to S$200,000 |
| 1 April 2029 | Existing businesses with annual supplies up to S$1 million |
| 1 April 2030 | Existing businesses with annual supplies up to S$4 million |
| 1 April 2031 | Existing businesses with annual supplies above S$4 million |
Output Tax and Zero-Rating Mistakes
A zero-rated sale has a 0% GST rate, but you can still claim input tax on costs related to that sale. Because this allows businesses to recover GST on those costs, IRAS requires proof that exported goods left Singapore or that a service meets the conditions for a zero-rating.
| Treatment | GST charged | Input tax on related costs | GST F5 box | Example |
| Standard-rated | 9% | Claimable | Box 1 | Most sales of goods and services in Singapore |
| Zero-rated | 0% | Claimable | Box 2 | Exported goods, qualifying international services |
| Exempt | None | Generally not claimable | Box 3 | Residential rent, certain financial services |
| Out-of-scope | None | Depends on the supply | Not in Boxes 1 to 3 | Goods bought and sold overseas that never enter Singapore |
Zero-rating exports without the right documents
For exported goods, you must meet a 60-day deadline: export the goods and keep the required documents within 60 days of the time of supply. These documents may include an export permit, bill of lading, or air waybill. If your customer arranges the shipping, you must also be sure at the time of supply that the goods will leave Singapore.
IRAS applies this rule strictly. In one published audit case, a company could not provide the required export documents, so IRAS treated the sales as standard-rated and recovered the GST. That is how an export worth S$500,000 can lead to a GST bill of about S$41,300: when a sale is treated as standard-rated after the fact, the price is treated as including GST, so 9/109 of the price is payable to IRAS.
When zero-rating is supported by the right documents, exporters may receive a GST refund each quarter, helping with cash flow. Keeping the documents helps show that the refund was claimed correctly.
Zero-rating services that do not qualify
Service zero-rating can be harder to assess. A service qualifies for 0% GST only if it meets one of the conditions in Section 21(3) of the GST Act. One common condition is that the customer belongs outside Singapore for GST purposes and directly benefits from the service outside Singapore. An overseas billing address alone is not enough. If the service directly benefits the customer’s Singapore branch or staff, it may still be subject to 9% GST.
The opposite mistake: charging 9% when 0% applies
Charging 9% GST when a sale should be zero-rated is also a mistake. Overseas customers cannot reclaim Singapore GST, so the extra charge may make your offer less competitive. To correct an overcharge, you may need to issue credit notes and file a GST F7.
We reviewed a case for an advertising agency whose previous accountant had applied the wrong GST treatment to its media sales. Our review identified sales that qualified for zero-rating (read the case study). Different rules for media sales have applied since 1 January 2022. Zero-rating now depends on where the customer and the direct beneficiary belong for GST purposes, not where the advertisements are shown.
Forgetting output tax on business assets
If you sell, give away, or use for private purposes a business asset on which you claimed GST, you usually need to account for output tax on it. Gifts that cost S$200 or less before GST are excluded from this rule. IRAS is also focusing on sales of non-residential property on which GST-registered sellers must charge GST.
Reverse Charge and Overseas Vendor Mistakes
Reverse charge can be easy to miss because an overseas supplier’s invoice usually does not show Singapore GST. It mainly applies to GST-registered businesses that cannot recover all their input tax, including banks, residential property developers, investment holding companies, and charities. Since 1 January 2020, these businesses have had to account for GST on imported services as if they had supplied the services themselves. Since 1 January 2023, the rule has also applied to low-value goods (items worth S$400 or less brought into Singapore by air or post).
| Worked example
A Singapore subsidiary pays its overseas head office S$1.2 million in royalties to use the group’s IT systems. It must account for S$108,000 in output tax (9%). Because it can recover 90% of the GST as input tax, it claims back S$97,200. The remaining S$10,800 is a real cost to the business. |
Many mistakes here involve transactions being left out of the return. For example, a business may omit an imported service because the overseas supplier did not charge GST, or overlook low-value goods bought online. Some unregistered businesses that cannot claim all their input tax may also be required to register. They may need to register if the total value of imported services and qualifying low-value goods subject to reverse charge exceeds S$1 million over 12 months.
Overseas sellers have a separate registration test. Under the Overseas Vendor Registration (OVR) regime, they must register if their global turnover exceeds S$1 million and their annual sales of remote services or low-value goods to customers in Singapore who are not GST-registered exceed S$100,000.
Filing and Payment Mistakes
Late filing triggers an automatic penalty. Your GST return and payment are due one month after the end of each accounting period. IRAS charges S$200 as soon as a return is overdue, then another S$200 for each full month it remains outstanding.
Other filing errors can be easier to miss:
- No nil return in a quarter with no activity. IRAS still requires one.
- Box 13 reports revenue and should be checked against your profit and loss account. If the figures do not match, explain the difference. For example, the accounts may include income from transactions that fall outside the scope of GST.
- Using different exchange rates in the GST return and the accounts.
- A GIRO payment fails because there are not enough funds in the bank account, and IRAS then cancels the GIRO payment plan.
- Closing the accounts too late to leave enough time to review the GST return before filing.
What each mistake can cost
| Situation | Penalty |
| Late filing | S$200 immediately, then S$200 for each completed month the return is outstanding, up to S$10,000 per return. IRAS may also issue an estimated assessment with a 5% late payment penalty. |
| Late payment | 5% of the unpaid tax. If still unpaid 60 days later, a further 2% for each completed month, up to 50% of the unpaid tax. |
| Incorrect return | Up to twice the tax undercharged. On conviction, a fine of up to S$5,000, up to three years’ imprisonment, or both. |
| Late registration | 10% of the GST due, plus a fine of up to S$10,000 |
| Charging GST while not registered | Three times the tax collected, plus a fine of up to S$10,000, up to three years’ imprisonment, or both |
| Qualifying voluntary disclosure | No penalty if the error is disclosed within the one-year grace period; otherwise, a 5% penalty on the tax underpaid (for qualifying disclosures) |
Late payment penalties can accumulate quickly. In IRAS’s example, a business with S$10,000 in unpaid GST incurs an extra S$1,300 after the 5% late-payment penalty and four monthly penalties of 2% each.
How to Fix a GST Mistake: Step by Step
Many GST errors can be corrected either in your next GST F5 return or by filing a GST F7 on myTax Portal. Two tests determine which option you must use. The S$3,000 limit often gets more attention, but the 5% test based on the value of supplies is just as important, as the example below shows.
Step 1: Check which correction route applies
| If… | Then… |
| The net GST error across all affected periods is S$3,000 or less, AND the value errors in each period are no more than 5% of total supplies (Box 4) | Adjust in your next GST F5 |
| If either test is not met | File a GST F7 for the affected period |
| The only error is revenue in Box 13 | No amendment is needed; use the correct revenue figure in future returns |
| The error is in pre-registration claims (Box 12) | File a GST F7 |
If you made no supplies during the period, use taxable purchases (Box 5) instead when applying the 5% test.
Step 2: Correct the return
- List each error by accounting period. Keep the GST amounts (Boxes 6 and 7) separate from the transaction values reported in the other boxes.
- Use IRAS’s GST F7 calculator to check both tests.
- If the error meets both tests, include the adjustment in your next GST F5 and keep your calculations on file.
- If the error does not meet both tests, request a GST F7 by going to File GST Return/Edit Past Return on myTax Portal. Submit the GST F7 within 14 days of requesting it, or the request will be deleted. A GST F7 replaces the original return, so enter the corrected figure for every box and explain what went wrong. You can combine errors from several accounting periods in the same year in one F7.
- Pay any additional GST using the payment details on the acknowledgement page.
- Fix the cause of the error, whether it was an incorrect tax code, an outdated invoice template, or a missing approval step.
| Worked example: F5 adjustment or F7?
A quarterly GST F5 left out a S$10,000 sale (S$900 GST) and a S$1,000 purchase (S$90 GST). Box 4 showed S$100,000 of supplies. • Net GST error: S$900 less S$90 is S$810, well within S$3,000. • Value errors: S$11,000, which is 11% of supplies and over the 5% limit. Result: despite the small GST amount, the business must file a GST F7. (Adapted from IRAS’s own example and updated to 9%.) |
Step 3: Disclose early
Under IRAS’s Voluntary Disclosure Programme, the penalty depends partly on when you disclose the error. Qualifying errors disclosed within one year of the filing deadline for the last GST return of that financial year carry no penalty. After that period, the penalty is 5% of the tax underpaid. If IRAS discovers the error before you disclose it, penalties can reach 200% of the tax underpaid.
For a disclosure to qualify, it must be made before IRAS asks about or audits the same issue. It must be complete and accurate, and you must pay the tax owed or agree to a payment plan. You can reclaim overpaid GST within five years from the end of the relevant accounting period.
GST Compliance Checklist: Do’s and Don’ts
You can prevent many of these errors with a few checks each quarter before preparing the return. Keeping your bookkeeping up to date makes these checks easier.
| Do | Don’t |
| Match every input tax claim to a tax invoice addressed to the business | Claim from quotations, statements or pro forma invoices |
| File export documents for each zero-rated sale as it ships | Zero-rate first and chase the paperwork later |
| Reconcile the GST return against the general ledger, and check that Box 13 agrees with revenue in the accounts | Assume the software’s GST report is correct |
| Have someone other than the preparer review the return | Let the person who prepared it approve it |
| File a nil return for any period with no business activity | Skip a return because there was no business activity |
| Disclose errors as soon as you find them | Wait to see whether IRAS notices |
| Update invoice templates and tax codes when rules change | Leave old GST rates in your accounting software |
IRAS’s Assisted Self-help Kit (ASK) annual review gives businesses a structured way to check past GST returns. If you find and disclose eligible errors through the review, you may qualify for penalty-free treatment.
When to Bring in Accounting Services in Singapore
Many small businesses manage GST themselves. Consider external help when your GST affairs become more complex, such as when you:
- Claim GST refunds in most quarters
- Export goods or provide services to overseas clients
- Make GST-exempt supplies and are subject to reverse charge
- Are deciding whether to register voluntarily
- Have found errors in past returns and need to correct them
Corporate Services Singapore’s accounting and tax teams can review how you handle GST, prepare and file your returns, and help correct past errors.
Frequently Asked Questions
How do I correct a GST mistake in Singapore?
Check whether the net GST error is S$3,000 or less and value errors are no more than 5% of total supplies. If both tests are met, adjust your next GST F5. Otherwise, request a GST F7 on myTax Portal and submit it within 14 days.
What happens if I make an error in my GST return?
Pay any GST owed. Qualifying voluntary disclosures made within IRAS’s one-year grace period carry no penalty; after that, a 5% penalty applies. If IRAS finds the error first, the penalty can reach 200% of the tax underpaid.
How do I reverse an input tax claim I made by mistake?
If the error meets both correction tests, reduce input tax in Box 7 of your next GST F5. Otherwise, file a GST F7 for the period in which you made the incorrect claim.
Why does my GST return not match my financial statements?
Timing differences, income outside GST’s scope, exchange-rate differences, and credit notes recorded in another period can cause mismatches. Reconcile your return to the general ledger and keep the reconciliation in case IRAS asks for it.
How far back can I correct a GST return?
Claim overpaid GST within five years from the end of the relevant accounting period. Disclose underpaid GST as soon as you find it; the penalty-free window lasts one year.
Can I cancel a voluntary GST registration?
Yes, but only after you have been registered for at least two years. When you cancel the registration, file a final GST F8 return and account for GST on any business assets you still hold, if required.
The Bottom Line
The most costly GST mistakes often start with a missing document or a filing error. Correct mistakes promptly, especially before the one-year penalty-free disclosure period ends. For help with a past GST return, a refund claim, or GST registration, speak to our team before your next filing deadline.
Sources
-
- IRAS – Recent GST Audits by IRAS
- IRAS – Current Areas of GST Audits
- IRAS – Are You Liable to Register for GST and What Happens If You Register Late
- IRAS – GST Registration Under the Prospective Basis
- IRAS – Factors to Consider Before Registering Voluntarily for GST
- IRAS – GST InvoiceNow Requirement
- GoBusiness – GST InvoiceNow Requirement
- IRAS – Conditions for Claiming Input Tax
- IRAS – Paying Suppliers After Claiming GST
- IRAS – Invoicing Customers
- IRAS – Foreign Currency Transactions
- IRAS – What Is Unauthorised GST Collection
- IRAS – Exporting of Goods
- MOF – Budget 2021 Annex F-1 (GST treatment of media sales)
- IRAS – GST: Reverse Charge (e-Tax Guide)
- IRAS – Overseas Businesses (Overseas Vendor Registration)
- IRAS – Late Filing or Non-filing of GST Returns
- IRAS – Late Payment or Non-payment of GST
- IRAS – Correcting Errors Made in GST Return (Filing GST F7)
- IRAS – Voluntary Disclosure of Errors for Reduced Penalties
- IRAS – GST General Guide for Businesses (e-Tax Guide)
