Auto-Inclusion Scheme enrolment and the annual cycle

Five employees is the number that quietly changes what a Singapore employer owes IRAS every year. Below it, filing income information is largely a matter between the employer, the employee, and the employee’s own tax return. At or above it, participation in the Auto-Inclusion Scheme becomes compulsory, and stays compulsory, on a calendar that runs from December’s payroll straight through to 1 March. This is not a form-by-form guide; our IR8A employer guide already covers Form IR8A and Appendices 8A and 8B in detail. This is the enrolment and the annual process around them: who has to join, how registration actually works, what the year looks like month by month, and what IRAS does about employers who miss it.

Who must register for AIS?

Participation in AIS is compulsory once an employer has had five or more employees at any time during the calendar year, a headcount test that counts full-time and part-time staff, non-resident employees, and any director who received remuneration, including anyone who left partway through the year. It is not a single snapshot on 31 December; it is measured across the whole year, so a company that briefly touched six employees in April and dropped back to three by year end is still in.

There is a second, independent trigger: receiving IRAS’s notice to file under AIS brings an employer in regardless of headcount. And once enrolled, an employer stays enrolled. Headcount falling back below five in a later year does not exit the scheme; AIS participation, once established, continues.

This catches out two kinds of employer in particular. A foreign company opening a lean Singapore office can cross five employees faster than expected once directors drawing remuneration are counted alongside the working headcount, and may not think of itself as “an employer with five staff” in the way a local SME would. And a company that grew past five, then restructured back down to three or four, often assumes the AIS obligation shrank with it. It did not.

How do you get in?

Registration runs through IRAS’s myTax Portal, via the “Register for AIS” e-service. For an employer newly crossing the threshold, registration and the subsequent submission both fall within the same annual window, closing on 1 March; employers typically submit employment income information in the run-up period from 1 February to 1 March.

Employers who stay under five employees and never receive an IRAS notice are not required to register or file electronically. They still carry an obligation, though a lighter one: hand employees hardcopy Form IR8A, and whichever appendices apply, by 1 March, so the employee can file their own personal tax return with accurate figures. Not being in AIS is not the same as having no obligation at all.

What the year actually looks like

The AIS year does not start in February. It starts in mid-January, on a date that has nothing to do with tax forms on its face: CPF submissions.

Under the AIS Data Link-up Service, IRAS pre-fills an employee’s employment income directly from what the employer has already submitted to CPF Board, but only for CPF contributions submitted by 14 January. A December contribution submitted after that date will not pre-fill into that year’s AIS return, and has to be added manually at IRAS’s digital service. For an employer running CPF submissions on schedule, this is invisible: the data simply appears. For an employer who runs a December submission late, it becomes an extra manual step discovered weeks later, by whoever handles AIS filing rather than whoever ran payroll in December.

From there, the window from 1 February to 1 March is when the actual income data goes in: salary, bonuses, benefits-in-kind and share options, filed as Form IR8A and the relevant appendices through the AIS channel. One exclusion worth knowing about: an employee who was cleared through IR21 tax clearance during the year, because they resigned and left Singapore, is excluded from that year’s AIS submission for the same income, to avoid reporting it twice. The two processes, IR21 for someone leaving mid-year and AIS for everyone still on payroll at year end, are built not to overlap.

Laid out on a calendar, the shape of an AIS year is this:

When	What is happening
All year	The five-employee headcount test runs continuously, not on one snapshot date.
By 14 January	December’s CPF contribution needs to be in, if it is to pre-fill automatically into this year’s AIS return.
1 February to 1 March	The submission window: employment income, benefits-in-kind and share option data go in through myTax Portal.
1 March	The deadline. Registered employers submit electronically; non-AIS employers under the threshold hand employees hardcopy Form IR8A instead.

Nothing on that calendar is complicated on its own. What makes it a genuine annual project, rather than a single afternoon, is that the January step depends on payroll discipline from the previous month, and the February step depends on data (benefits-in-kind, share options) that often lives with someone other than whoever runs monthly payroll.

What happens if you get it wrong

Missing the 1 March deadline is an offence under the Income Tax Act 1947, carrying a fine of up to S$5,000 under section 94(1). Directors, precedent partners or key management personnel who ignore IRAS’s own notices can face a personal fine of up to S$10,000 and/or up to 12 months’ imprisonment, a considerably sharper consequence reserved for employers who do not respond at all rather than for a routine late filing.

IRAS has published real enforcement figures, and they are worth stating plainly, without embellishment: for Year of Assessment 2023, IRAS reported that over 900 employers were prosecuted for AIS non-compliance, with penalties exceeding S$1 million in total. Those are two separate totals IRAS chose to publish. Dividing one by the other to produce an average penalty per employer would be an invented figure, not an IRAS statistic.

What to keep on file afterwards

Submitting on 1 March does not close the file. Records supporting income and expense claims, payroll among them, must be kept for at least five years from the relevant Year of Assessment under the Income Tax Act 1947, produced to IRAS on request rather than filed away and forgotten. For a company in its first year of AIS, this is worth setting up properly from the start: a labelled folder per Year of Assessment, holding the submission itself, the underlying payroll reconciliation, and any correspondence with IRAS, saves a scramble if a query arrives three years later about a submission nobody on the current team remembers making.

Where AIS ends and the forms begin

AIS is the channel, not the content. What actually goes through it, Form IR8A, Appendix 8A for benefits-in-kind, Appendix 8B for share options, and how Form IR8S folded into the main IR8A from Year of Assessment 2026, is covered in full on our IR8A employer guide. This page is about getting registered, getting the calendar right, and knowing what happens when the 1 March window closes on an employer who was not ready.

First year in the scheme

Crossing five employees for the first time often coincides with needing a proper HR function for the first time too, not just a tax registration. If that is where your company is, see how we support HR set-up for employers building the function from scratch, including the wider Singapore payroll compliance calendar that AIS sits inside alongside CPF, SDL and IR21.

For the AIS side specifically, we run payroll processing, including the monthly CPF submission discipline that the 14 January cut-off quietly depends on. A first-time filer can equally do this alone. The threshold test and the registration route are both set out above; what neither of them will do is remind you that the work belongs in January rather than in the last week of February.