For most groups, determining if they are an Applicable Large Employer (ALE) is done at the end of one calendar year to determine if they will be an ALE for the next calendar year.
For example, towards the end of 2024, an employer will determine if they averaged 50 or more full-time equivalent employees during 2024. If they did, then they will be an ALE in 2025. If an employer averages less than 50 full-time equivalent employees during 2024, then they would not be an ALE during 2025.
Please see the section on determining ALE status on the attached ACA Employer Guide starting on page 7.
If a group is involved in a merger or acquisition, then it is possible for them to become an ALE as of the date that the M&A occurred.
Also, if a new company starts up today, with 50+ employees, then they could be an ALE as of 1/1/2025, even though they did not average 50+ full-time equivalent employees during all of 2024. Instead, they could average 50+ full-time equivalent employees for their working days during 2024.
Here is the text from IRS Regulation §54.4980H-2 Applicable large employer and applicable large employer member.
(a) In general. Section 4980H applies to an applicable large employer and to all of the applicable large employer members that comprise that applicable large employer.
(b) Determining applicable large employer status.
1) In general. An employer's status as an applicable large employer for a calendar year is determined by taking the sum of the total number of full-time employees (including any seasonal workers) for each calendar month in the preceding calendar year and the total number of FTEs (including any seasonal workers) for each calendar month in the preceding calendar year, and dividing by 12. The result, if not a whole number, is then rounded to the next lowest whole number. If the result of this calculation is less than 50, the employer is not an applicable large employer for the current calendar year. If the result of this calculation is 50 or more, the employer is an applicable large employer for the current calendar year, unless the seasonal worker exception in paragraph (b)(2) of this section applies.
(2) Seasonal worker exception. If the sum of an employer's full-time employees and FTEs exceeds 50 for 120 days or less during the preceding calendar year, and the employees in excess of 50 who were employed during that period of no more than 120 days are seasonal workers, the employer is not considered to employ more than 50 full-time employees (including FTEs) and the employer is not an applicable large employer for the current calendar year. In the case of an employer that was not in existence on any business day during the preceding calendar year, if the employer reasonably expects that the sum of its full-time employees and FTEs for the current calendar year will exceed 50 for 120 days or less during the calendar year, and that the employees in excess of 50 who will be employed during that period of no more than 120 days will be seasonal workers, the employer is not an applicable large employer for the current calendar year. For purposes of this paragraph (b)(2) only, four calendar months may be treated as the equivalent of 120 days. The four calendar months and the 120 days are not required to be consecutive.
https://www.law.cornell.edu/cfr/text/26/54.4980H-2
In English, what this means is that each calendar year an employer needs to make a determination if they will be an Applicable Large Employer (ALE) for the next calendar year. An employer would look at their employee count in 2023 to determine if they are an ALE effective 1/1/2024. If they are an ALE in 2024, then by March 1, 2025, they are required to distribute Form 1095-C to their full-time employees, and by March 31, 2025, electronically submit Form 1094-C to the IRS along with copies of the Form 1095-C’s.
For each month during 2023, the employer would determine how many full-time employees they had during the month. A full-time employee is someone who averaged working at least 30 hours per week during that month or worked at least 130 hours during that month.
They would also determine how many full-time equivalent employees. To make that determination, the employer would add up all of the hours worked by non-full-time employees, and divide by 120. If those part-time employees had worked 1,200 hours during a month, that would equal 10 full-time equivalent employees. [1200 / 120 = 10]
For each month they would add the full-time and full-time equivalent employees together to get that months total.
They do that for each month.
Then they add up the totals for each month and divide by 12, that provides the monthly average.
If the monthly average is 50 or greater for a calendar year, then they would be an ALE for the next calendar year.