Federal law places no limit on how many hours a per diem employee can work in a day or a week. The Fair Labor Standards Act sets no maximum for workers aged 16 and older, and there is no separate category in the law for per diem status.1U.S. Department of Labor. Wages and the Fair Labor Standards Act What the law does instead is attach consequences to specific hour thresholds: overtime pay after 40 hours in a week, a health coverage obligation at 30 hours, family leave eligibility at 1,250 hours in a year, and retirement plan access at 500 or 1,000 hours. Those thresholds, more than any statute, are what actually shape per diem schedules.
Overtime Starts at 40 Hours in a Workweek
If your employer asks you to work 50, 60, or 70 hours in a single week, federal law allows it. The constraint is pay, not scheduling. Once a non-exempt employee crosses 40 hours in a workweek, every additional hour must be paid at one and a half times the regular rate.2U.S. Department of Labor. Overtime Pay
A workweek is a fixed, recurring period of seven consecutive 24-hour days. It can start on any day and any hour, but once the employer sets it, the period stays consistent. Averaging hours across two or more weeks to avoid overtime is not permitted.3U.S. Department of Labor. Fact Sheet #23: Overtime Pay Requirements of the FLSA An employer cannot combine a 50-hour week with a 30-hour week and call the average 40.
Most per diem workers are paid hourly and are non-exempt, which means overtime applies. Some per diem professionals paid on a salary or fee basis may fall under a white-collar exemption if the duties test is met and pay reaches the DOL’s minimum threshold.4U.S. Department of Labor. Fact Sheet #17N: Nurses and the Part 541 Exemptions Under the FLSA Hourly per diem nurses, for example, should receive overtime regardless of their professional credentials.
The 30-Hour ACA Threshold Is Why Many Employers Cap Shifts
The Affordable Care Act is the single biggest reason employers watch per diem hours closely. Any employer with 50 or more full-time equivalent employees must offer health insurance to workers who average at least 30 hours per week, or 130 hours per month.5Internal Revenue Service. Determining if an Employer Is an Applicable Large Employer If those workers do not receive an offer of qualifying coverage, the employer faces penalties.
For 2026, the penalty amounts are:
- $3,340 per full-time employee per year (minus the first 30 employees) when no coverage is offered and at least one full-time employee receives a premium tax credit through the marketplace.6Internal Revenue Service. Rev. Proc. 2025-26
- $5,010 per year for each full-time employee who enrolls in a subsidized marketplace plan because the coverage offered was unaffordable or inadequate.6Internal Revenue Service. Rev. Proc. 2025-26
Those numbers explain why many hospitals, staffing agencies, and school districts quietly cap per diem shifts at 29 hours per week. Extending health coverage to a rotating pool of per diem staff is expensive, and the penalty adds up fast across dozens of employees.
The Look-Back Measurement Method
Because per diem schedules fluctuate, the IRS allows employers to use a look-back measurement method rather than tracking hours in real time. The employer picks a measurement period between 3 and 12 consecutive months, then averages your hours over that window. If the average hits 30 or more hours per week, the employer must treat you as full-time for a corresponding stability period and offer coverage. For new hires with unpredictable schedules, a separate initial measurement period of 3 to 12 months applies.7Internal Revenue Service. Notice 2012-58
A few heavy weeks will not automatically make you full-time under this system. But consistently picking up extra shifts over several months can. If your employer uses a 12-month measurement period, you might not know you have crossed the threshold until the calculation runs, at which point the employer either offers coverage or cuts your hours going forward.
1,250 Hours in a Year for FMLA Leave
Per diem workers can qualify for job-protected leave under the Family and Medical Leave Act, but the eligibility bar is steeper than many realize. You need to have worked for the employer for at least 12 months and logged at least 1,250 hours during the 12 months before your leave starts.8U.S. Department of Labor. Family and Medical Leave (FMLA) Your employer must also have at least 50 employees within 75 miles of your worksite.9U.S. Department of Labor. Fact Sheet #28: The Family and Medical Leave Act
The 1,250-hour requirement works out to roughly 24 hours per week over a full year. A per diem worker averaging 15 to 20 hours will not get there. This is where a per diem arrangement’s flexibility can work against you: sporadic shifts may never add up to enough hours for the 12 weeks of unpaid, job-protected leave FMLA offers.
1,000 Hours for Pensions, 500 Hours for 401(k) Access
Federal law sets a floor for when an employer’s retirement plan must let you in. A plan generally cannot exclude you once you have completed a year of service, defined as a 12-month period in which you work at least 1,000 hours.10Office of the Law Revision Counsel. 29 U.S. Code 1052 – Minimum Participation Standards That is roughly 19 hours per week over a year. Per diem employees who stay below that threshold can be excluded from the plan.
A newer rule changes the math for 401(k) plans specifically. Long-term part-time employees who work at least 500 hours in each of two consecutive 12-month periods must be allowed into their employer’s 401(k) plan once they turn 21, for plan years beginning after December 31, 2024.10Office of the Law Revision Counsel. 29 U.S. Code 1052 – Minimum Participation Standards The IRS has confirmed the final regulation applies no earlier than plan years beginning on or after January 1, 2026.11Internal Revenue Service. Notice 2024-73 For a per diem worker averaging 10 hours a week, 500 hours is reachable, and it opens access to employer-sponsored retirement savings that was previously out of reach.
State Rules Add Their Own Limits
Federal law is the floor. State and local rules add layers that directly shape per diem scheduling, and they vary widely.
A handful of states require overtime pay when a single shift exceeds a set number of hours, typically eight, regardless of total weekly hours. That daily overtime rule changes the calculus for per diem workers covering long shifts in healthcare or hospitality. Several states also mandate paid rest breaks and unpaid meal periods of at least 30 minutes for shifts above a certain length.
A growing number of cities and states have adopted fair workweek or predictive scheduling laws, primarily in retail, food service, and hospitality. These typically require employers to post schedules at least 14 days in advance and pay a premium when shifts are changed, added, or canceled inside that window. Per diem work relies on short-notice scheduling by nature, which creates tension with these laws. Whether one covers your situation depends on the industry, employer size, and jurisdiction.
Some states also require reporting time or show-up pay: if you arrive for a shift and it is canceled or cut short, the employer must pay a minimum number of hours anyway, typically two to four at your regular rate. And more than 20 states now require paid sick leave, with a typical accrual rate of one hour for every 30 hours worked. Because accrual is tied to hours on the clock, per diem employees earn leave proportionally. A few states explicitly exclude certain per diem categories, such as per diem nurses in at least one state, so the specifics matter.
Employer Policies Are the Real Ceiling
Beyond what the law requires, individual employers set their own rules. In healthcare, hospitals commonly let per diem nurses and aides select shifts from an open board based on patient census and staffing needs. In education, substitute teachers are called on short notice when regular staff are absent. These systems look different, but most share a few features.
Employers typically require per diem workers to submit availability windows in advance, sometimes weekly, sometimes monthly. Many set a minimum number of shifts per scheduling period to keep you on the active roster. Some cap total hours at 29 per week to stay below the ACA threshold. Others allow up to 40 but flag anyone approaching overtime. Employment handbooks or onboarding documents usually spell out these rules, along with policies on shift swaps, cancellation notice, and how far in advance you can claim open shifts.
These internal policies are where per diem hours actually get limited. Federal law will not stop you from working 60 hours in a week, but your employer’s benefits strategy and scheduling software almost certainly will. If you want more hours, the leverage point is usually the staffing coordinator, not the statute.