By KYN AI Advisory Team — AI implementation specialists, Singapore
You must register for GST in Singapore when your taxable turnover is more than $1 million. IRAS tests this two ways: looking back at the last calendar year (retrospective) and looking forward over the next 12 months (prospective). If you cross either test, you apply within a fixed window, and from the registration date your invoices must carry GST. This article sets out both tests, the deadlines, voluntary registration and what changes in your invoicing.
What counts toward the $1 million?
IRAS defines taxable turnover/gst-registration-deregistration/do-i-need-to-register-for-gst) for registration as your sales that are standard-rated or zero-rated. It excludes exempt supplies, out-of-scope supplies, and sales of capital assets. A company that sells mostly exempt items, such as certain financial services, can have high revenue and low taxable turnover.
What is the retrospective test?
Add up taxable turnover for 1 January to 31 December. If it exceeded $1 million, you must apply for GST registration between 1 January and 30 January of the following year. Registration takes effect on 1 March of that year.
If the turnover exceeded $1 million but you do not expect it to exceed $1 million over the next 12 months, you are not required to register immediately. IRAS expects you to support that view.
What is the prospective test?
At any time, if you can reasonably expect taxable turnover to exceed $1 million in the next 12 months, you must apply within 30 days after the date of your forecast. For forecasts made on or after 1 July 2025, registration takes effect two months after the forecast date. For earlier forecasts it was the 31st day. The 30-day application deadline did not change.
IRAS requires the forecast to rest on evidence, such as signed contracts. A forecast built only on a market assessment, a business plan or a sales target does not trigger registration.
| Test | Looks at | Apply by | Effective | |---|---|---|---| | Retrospective | Calendar year just ended | 1 to 30 January | 1 March | | Prospective | Next 12 months | 30 days after the forecast | 2 months after the forecast (from 1 July 2025) |
All dates and rules above are from IRAS's registration page/gst-registration-deregistration/do-i-need-to-register-for-gst), checked 30 October 2026.
What happens if you register late?
Registration is backdated to the date you ought to have registered. You must account for GST on past sales from that date. Fines and penalties may apply, though IRAS says they are generally waived if you voluntarily disclose the lateness on your application.
The practical risk: you cannot add GST to invoices already issued without asking customers to pay more. Late registration often means the business absorbs the GST amount out of its own margin.
Should you register voluntarily below the threshold?
IRAS allows voluntary registration if you meet the conditions on its page about factors to consider. The trade-offs:
| | Registered | Not registered | |---|---|---| | Charge GST on sales | Yes | No | | Claim GST on purchases (input tax) | Yes, with valid tax invoices | No | | Filing | A GST return each period, even nil | None | | Customers | Business customers recover GST; consumers pay more | Price is the price | | Admin | Tax invoices, records, workings | Less |
Register voluntarily when most of your customers are GST-registered businesses and you have large GST-bearing purchases, such as equipment or inventory. Do not register if your customers are mostly consumers and your purchases are light, because you will either raise prices or take a margin cut, and gain little input tax.
How do your invoices change after registration?
From the effective date:
- Issue tax invoices showing your GST registration number, the word "Tax Invoice", the date, a description, the amount before GST, the GST charged and the total.
- Charge GST at the standard rate on taxable supplies, or zero-rate qualifying exports.
- Keep copies, because records back your return. IRAS requires companies to keep records for at least five years. See what to keep.
- Claim input tax only on valid tax invoices addressed to your business. Read how to scan receipts for GST claims.
- File a return after each accounting period. The return and payment are due one month after the period ends/filing-gst/due-dates-and-requests-for-extension), and a nil return is still required.
Check the exact content rules for a tax invoice on the IRAS site before you build a template.
How do you monitor the threshold?
Do not check once a year. Monitor monthly.
- Tag each sale in the ledger as standard-rated, zero-rated, exempt or out of scope.
- Compute taxable turnover for the calendar year to date and for the trailing 12 months.
- Compare to the threshold and show it as a number and a percentage of the threshold.
- Alert a named person at 70% and 90% of the threshold, and when a signed contract would take the forecast over.
- Keep the evidence for any forecast you choose not to treat as triggering registration.
The 70% and 90% levels are our suggestion, not an IRAS rule. They give you time to prepare invoicing, pricing and systems.
What does the forecast evidence look like?
IRAS says the prospective test rests on evidence such as signed contracts, not on targets. In practice, keep a short file for each decision date:
- the contracts or confirmed orders with value and delivery dates;
- your sums for the next 12 months of taxable turnover, split by contract and by recurring sales;
- the date you ran the test and who ran it;
- the conclusion: register, or no registration required, and why.
If a contract is signed but its value is uncertain, take the conservative figure and note it. If a new contract takes the total over $1 million, the 30-day clock starts from the date you made the forecast, so run the test the day you sign. Waiting for the next month-end gives you less time than you think.
How does GST change cash flow?
Registration adds a quarterly cycle. You collect GST from customers, pay GST to suppliers, and hand the difference to IRAS one month after each period. If customers pay slowly, you may owe IRAS the output tax before you have received it. Plan cash for that gap, and follow customers up on schedule; see the 3, 14, 30 day chase schedule.
What should you prepare before the registration date?
- Your accounting software set up with GST codes and rates.
- Updated quote and invoice templates.
- A pricing decision: add GST on top, or absorb it.
- Customer notices that prices will show GST.
- A calendar of return dates. See the 2027 corporate tax deadlines.
- A person assigned to review each return.
Where KYN fits
KYN builds finance systems in a cloud account in your name. In our own books, GST is tracked by quarter. A system can tag sales by tax treatment, compute taxable turnover on both IRAS tests each month and alert a named person well before the threshold. Registration and filings involve a government submission, so they wait for a named person, and every action is logged with the actor.
The 14-day review checks how sales are tagged by tax treatment and where turnover is recorded. A full build ships in under 90 days. See finance systems.
Frequently asked questions
Does the $1 million include sales outside Singapore?
It includes taxable supplies, which covers zero-rated supplies such as qualifying exports. It excludes exempt supplies, out-of-scope supplies and sales of capital assets. Check how your overseas sales are classified before you test the threshold.
Can I cancel GST registration later?
Yes, if you meet IRAS's conditions for deregistration. Voluntary registrants face a minimum period before they may cancel, so check the current rule on IRAS before you register voluntarily.
What if I only just crossed $1 million on one large sale?
Apply the retrospective test at year end and the prospective test now. If the sale was one-off and next year's taxable turnover will stay under $1 million, IRAS's retrospective rule says you are not required to register immediately. Keep the evidence for that view.
Checked 30 October 2026.
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