Variable-hour and seasonal employees: how the ACA look-back measurement method works.
Who counts as full-time when hours move around, how the measurement, administrative and stability periods fit together, and where employers get tripped up. Written for the owner or HR lead.
Why Hours Are Measured at All
Employers with fifty or more full-time employees, counting full-time equivalents, must offer affordable coverage to the full-time group or face a penalty. For employees whose hours do not follow a schedule, the law gives a method for deciding who is full-time before the year is over.
Who It Applies To
Applicable large employers: those that averaged fifty or more full-time employees, including full-time equivalents, in the prior calendar year. Related companies under common ownership are counted together. Counting depends on hours and ownership structure, so employers near the line should run the numbers carefully each year. If you are part of a group of related companies, ask your tax adviser or counsel how the combined count applies.
Why It Exists
Hours that swing month to month would otherwise force a coverage decision before anyone knows whether the employee is full-time. The look-back method lets you measure first and then hold the result steady. Without it, an employer might offer coverage to everyone to be safe, or guess wrong and miss someone. A written method gives you a consistent, defensible way to decide who gets an offer and when.
What It Is Not
It is not a waiting-period rule and it does not change who your plan terms make eligible. It decides who counts as full-time for the employer mandate and for the offer-of-coverage reporting. Employers often confuse the two and apply an ACA measurement result to plan eligibility, or the reverse. Keep them as two separate questions in your documents and administration, and check both before you tell an employee where they stand.
Full-Time, Part-Time, Variable-Hour and Seasonal
The labels in a handbook do not decide any of this. Hours of service do.
Full-Time Employee
An employee averaging at least thirty hours of service a week, or one hundred thirty hours in a calendar month, is full-time for the employer mandate. The thirty-hour test is based on hours of service, which include paid time off as well as time worked. Hours for each month or measurement period should come from a payroll record you can produce if the IRS asks.
Variable-Hour Employee
An employee for whom, at the start date, you cannot reasonably tell whether the average will reach thirty hours a week. The test is what a reasonable employer would expect at hire, not what happens later. Typical examples include seasonal staff, on-call workers and employees whose schedules depend on demand. Document the reasoning at hire, because an employer cannot choose the label after seeing the hours.
Seasonal Employee
An employee in a position for which the customary annual employment is six months or less, such as a holiday retail or summer resort job. Year-round staff with a busy season generally do not qualify. Decide at hire whether a position truly fits this definition, and write the reasoning down. If a role is unclear, ask your benefits adviser.
Part-Time Employee
An employee reasonably expected to average under thirty hours. Expectation is judged at hire and revisited as the facts change, so a “part-time” title that works full-time hours is still a full-time employee. Review each part-time worker’s actual hours regularly, since schedules that grow over time can change the right classification. Titles and handbook labels do not control the outcome, so rely on the hours and the facts instead.
Three Periods, Always in the Same Order
Measure, then pause to administer, then hold the result steady. Each period has a legal range.
Measurement Period
A stretch of three to twelve consecutive months in which you total each employee’s hours. You choose the length, and the choice should reflect how much your hours actually swing. A longer period smooths out big swings but delays the result, while a shorter one reacts faster. Pick the length based on your own scheduling patterns and the enrollment calendar, and apply it to the whole category the same way.
Administrative Period
Time to run the numbers, notify employees, enroll them and start coverage. It cannot exceed ninety days, and it is where an overlong process quietly breaks the rules. Work backward from the plan year start and give payroll, HR and the carrier enough time. Many employers lose days to slow data pulls, so test the process on a trial run before the real measurement period closes.
Stability Period
The stretch in which the result holds. An employee found full-time stays full-time for the whole period, even if hours fall. It must run at least six consecutive months and be no shorter than the measurement period. Because the status holds even when hours drop, keep offering coverage through the end of the period. Track end dates for each employee so one period flows into the next without gaps.
Ongoing Employees and New Employees Run Separately
Most mistakes come from using one track for the other.
Ongoing Employees
Everyone who has completed a standard measurement period is measured on the same calendar every year, with the new stability period starting right after the administrative gap. Many employers line the stability period up with the plan year so the result follows open enrollment.
New Variable-Hour, Seasonal and Part-Time Employees
A new hire gets an initial measurement period of up to twelve months starting at the start date or the first of the following month. The initial measurement period plus the administrative period cannot run past the end of the first month that begins on or after the one-year anniversary.
What Counts as an Hour of Service
The hour count is where most disputes with the IRS letter start.
Paid Leave Counts
Vacation, holiday, sick time and other paid leave are hours of service even when no work was done. Leaving them out understates the count. Also count hours for any paid time off recorded by payroll, even when no work was done. Check that your timekeeping system includes those hours in the totals it reports for ACA measurement, not only hours worked.
Employees Without Time Records
For salaried or commissioned staff, the rules allow actual hours, a days-worked equivalency of eight hours a day, or a weeks-worked equivalency of forty hours a week. The method has to be applied consistently to the category. Pick one method for each category and apply it to everyone in it. Ask your benefits adviser which approach fits your pay structure, since an equivalency can overstate or understate some employees’ hours.
Special Unpaid Leave
Unpaid FMLA leave, jury duty and military leave are treated so they do not drag an average down: the period is excluded or credited at the employee’s average. Other unpaid leave is not neutralized. The rules for these leaves are technical, so check how your system records them and ask counsel or your benefits adviser about unusual cases. Keep supporting records, such as leave notices, so the treatment can be explained later.
Four Places Employers Get It Wrong
None of these is exotic. They show up in notices from the IRS about year-end reporting.
A Measurement Window That Misses Open Enrollment
If the administrative period ends in March but the plan year starts in January, someone found full-time has no way in. Build the calendar backward from plan-year start. Test the timeline with an example hire date and see when the offer would actually start. If the dates do not line up, adjust the measurement or administrative period instead of hoping employees will not notice the delay.
Offering Coverage Late
An employee identified as full-time must be offered coverage for the whole stability period. A late offer leaves months where the employer is exposed to a penalty, even if the plan eventually enrolled the employee. Missed deadlines usually come from slow data pulls or unclear ownership. Assign an owner to each step, set internal deadlines ahead of the real ones, and keep records of when each offer went out.
One Method for Every Category
Hourly, salaried, union and different-state groups can use different periods, but only if each category is written down in advance. A new category introduced mid-year needs its own election. Keep the written election with your plan records and update it before you make changes, not after. If categories overlap or employees move between them, ask your benefits adviser how to apply the rules for that situation.
Rehires and Breaks in Service
A break of at least thirteen consecutive weeks, 26 weeks for educational organizations, lets an employer treat a returning employee as new. A shorter break generally carries the earlier status forward. Returning employees are easy to mishandle, because payroll may treat them as new while the ACA rules treat them as continuing. Track departure and return dates in one place and ask your adviser about edge cases.
Look-Back or Monthly Measurement
The law also allows a monthly test, and it can be the better answer for a workforce whose hours barely move.
Monthly Measurement
Each month stands alone. It is easy to run and simple to explain, but an employee near thirty hours can flip status month to month, and you owe an offer in each month they are full-time. This method suits employers with stable schedules and simple payroll, but status can change often, which creates more offers and notices to manage. Compare it with the look-back method before choosing.
Look-Back Measurement
The result holds for the stability period. It takes calendar discipline and an hours-tracking source you trust, and in return it removes the churn. It also gives employees and HR a predictable schedule of decisions. Many employers prefer it for variable workforces, but it still needs written policies and regular checks that hours were measured correctly and offers followed the results.
The Decisions That Belong in a File
If an IRS letter arrives, the file is the defense.
The Election by Category
Which employees are on which method, the length of each period, and the dates they start and end. Write it down before the first measurement window opens. Keep this election with your plan records and share it with payroll, the carrier and anyone who prepares ACA filings. A record that is easy to find makes an IRS letter or an internal audit far less painful to answer.
The Hours Source
Which payroll or timekeeping system produced the totals, and how non-hourly staff are counted. Changing the source mid-period needs a note. Record the report name or system used, who pulled it and when. If you change vendors or move to a new payroll platform, document how the hours were carried over so the measurement period stays consistent and defensible.
The Employee Notice
What each employee was told about their status and when. A clear notice also reduces the questions that land in HR. Keep a copy of the notice with the date it was sent and the method of delivery. If an employee later says they were not told, a dated record of what was communicated is the best way to settle the question.
The questions that come before the first measurement window.
Six questions employers bring us about variable-hour measurement.
Do we have to use the look-back method?
No. The monthly measurement method is also allowed, and some employers use one for hourly staff and another for salaried. Whichever you pick must be applied consistently to its category.
Can we change the measurement period each year?
The standard measurement period is generally set for the category and kept steady. Changing it is possible, but the change has to be deliberate and documented, and it can create overlap problems with the prior stability period.
What if an employee’s hours jump mid-stability period?
Nothing changes for the mandate until the next measurement. An employee identified as not full-time can stay that way for the stability period, and a full-time employee whose hours fall stays full-time until it ends.
How does this relate to our plan’s waiting period?
They are separate. A plan can set its own eligibility rules, but the waiting period cannot exceed ninety calendar days, and a plan that is stricter than the mandate can still leave you exposed.
Are seasonal employees ever exempt from the mandate?
They are not exempt. They are simply measured. If a seasonal employee averages thirty hours across the initial measurement period, the employer owes an offer during the stability period.
What does the IRS look at if we get a letter?
The offer of coverage, the affordability of the lowest-cost option and the full-time determination. The measurement file is how you show the third one.
Ready? Send us your renewal, or talk it through with someone first. No cost, no obligation.
General information about ACA employer-mandate measurement, not legal advice. Penalty exposure and plan-specific questions belong with benefits counsel, and we will bring them in.
Related guides.
Agriculture and Farm Employers
Benefits for seasonal, migrant and year-round workers.
Staffing Agencies
Benefits for temporary and placed employees.
Construction and Skilled Trades Employers
Benefits around seasonal work, crews that move and union agreements.
Trucking and Transportation Employers
Health benefits for drivers on the road, owner-operators and dispatch teams.
Independent Contractors and Leased Workers
Worker status, plan eligibility, the ACA count and what misclassification costs.
Rehired Employees and Breaks in Service
When coverage restarts for a returning employee and when a waiting period applies again.
Waiting Periods for Group Health Coverage
The 90-day limit, common waiting period designs, and the first-of-the-month trap.
ACA Reporting Guide
Forms 1094-C and 1095-C, with the codes that depend on measurement.
Measurement Period Calculator
Work out your own dates before the window opens.
Michigan Employer Benefit Laws
The state rules that sit next to the federal ones.
Send us your renewal.
We’ll tell you whether it looks competitive, where we see opportunity, and the five questions we’d put to your carrier. No cost, and no obligation to move anything.
The renewal letter
Your current plan summary
Contribution split by tier
Enrolled counts by tier
Four documents — two more if your group is 50 or more. Nothing else; every extra one is a reason to postpone.
Laws and rules referenced
26 C.F.R. § 54.4980H-1 — Definitions, including full-time employee, seasonal worker and how employees are counted.
26 C.F.R. § 54.4980H-3 — Determining full-time employees: monthly and look-back measurement methods.
This page is general information, not legal or tax advice. Rules change and facts matter, so confirm your situation with counsel or a qualified advisor.
An independent employee benefits consulting firm. We look at the entire benefits program — cost, plan performance, risk and administration.
Switch to CFH. Unhappy with your broker? Your employees won’t notice. You will. →
Cookies on This Site
We use cookies to keep the site working properly and to understand how it is used. You can decline anything that is not essential. See our Privacy Policy for the detail.
- Essential — needed for the site to load and for you to move around it. These cannot be switched off.
- Analytics — tell us which pages get read, so we know what is worth writing more of.
- Advertising — set by third parties such as ad and social platforms to measure and target campaigns.