Per Diem Work

Per diem work is employment where someone works only when the employer needs them, shift by shift, with no guaranteed hours. The term is American and most common in healthcare, where the same arrangement is called PRN, from the Latin pro re nata, "as the situation requires". A per diem nurse or substitute teacher is on the payroll, but only works the shifts they accept.

What is per diem work?

Per diem work is an employment arrangement in which the employer offers shifts when it needs cover and the employee decides which ones to take. There is no fixed schedule and no promise of a minimum number of hours. The employee is paid for the hours actually worked, usually at an hourly rate, through the normal payroll.

Per diem is Latin for "per day", and that is why the same words also mean something else: a daily travel allowance for meals and lodging on a business trip. A per diem employee is a type of worker. A per diem allowance is an expense payment that any employee, full-time or not, can receive when travelling. This page is about the worker, and the one place where the two meet, overtime pay, comes up under the US rights below.

How per diem shifts work in practice

The employer keeps a pool of per diem staff next to its regular team. When a gap opens, because someone is off sick, on holiday or the weekend is busier than planned, the shift goes out to the pool and whoever is available and qualified picks it up. Some employers post shifts weeks ahead. Others ring round on the morning itself.

The law sets no rules for how often a per diem employee has to work, so most employers set their own. Common ones are a minimum number of shifts per month or quarter, one weekend or bank holiday shift in each scheduling period, and a notice period for cancelling a shift that was already accepted. Someone who takes no shifts for several months is usually taken off the list. These are policies, so they belong in the offer letter or per diem agreement where both sides can read them.

Take a care home with 40 beds. The regular team covers the planned schedule and eight per diem care assistants cover the rest. In one week in February, three regular staff call in sick and one is on holiday, which leaves eleven shifts open. The manager posts all eleven on Monday morning. By Tuesday, five people from the pool have taken nine of them, and the last two go to regular staff as overtime. Without the pool, all eleven would have been overtime or agency shifts.

The same set-up runs in a restaurant with a summer terrace, a shop in the weeks before Christmas or a hotel that hosts weddings at the weekend. Only the size of the pool and the notice period change.

How many hours can a per diem employee work?

No US law caps the hours of a per diem employee as such. The limits come from the employer's own policy and from two lines in federal law that make extra hours more expensive:

• Above 40 hours in a workweek, the Fair Labor Standards Act requires overtime at one and a half times the regular rate. The workweek is a fixed period of 168 hours, and hours cannot be averaged over two weeks. A per diem employee who works 50 hours one week and 20 the next is owed 10 hours of overtime for the first week.

• At an average of 30 hours a week, or 130 hours a month, an employee counts as full-time under the Affordable Care Act. For an employer covered by the Act's employer rules, that brings the obligation to offer health coverage. The IRS lets employers measure hours over a look-back period and fix the status for a following period, which suits staff whose hours go up and down.

Many employers cap per diem hours themselves, for example at 24 hours a week, so the pool does not turn into a part-time team without part-time terms. In the UK the Working Time Regulations apply: no more than 48 hours a week on average, unless the worker has opted out in writing.

Per diem, part-time, full-time and zero-hours compared

The difference between per diem and part-time is the commitment. A part-time employee has a set number of hours and a regular schedule. A per diem employee has neither and accepts shifts as they come. Part-time staff in the US often get some benefits pro rata, while per diem staff usually get a higher rate and no benefits. The overview of types of employees sets both next to temporary and contingent staff.

Per diem employee rights in the US

A per diem employee is an employee. The Department of Labor decides status on the economic reality of the relationship, and what the worker is called is not relevant. A per diem nurse who works the hospital's shifts, on its wards, under its supervision, is an employee whatever the contract calls them. Treating per diem staff as independent contractors to save on tax and overtime is misclassification.

That gives per diem employees the same core rights as the rest of the team. They are owed at least the minimum wage for every hour and overtime above 40 hours in the workweek. State and city employment laws apply to them as to any other employee, so check paid sick leave and daily overtime rules where the work is done. And once their average hours reach 30 a week, the Affordable Care Act counts them as full-time.

What the law does not give them is guaranteed hours, or a place in the employer's health, pension or paid time off plans while they stay below those lines. That is the trade-off of the arrangement, and it is why per diem rates are often higher than staff rates for the same job.

Travel nurses and field staff sometimes get both kinds of per diem: per diem shifts and a per diem allowance for meals and lodging. Under 29 CFR 778.217, an expense payment stays out of the regular rate for overtime only if it reasonably approximates the expense. Allowances within the federal per diem rates count as reasonable for travel. When an allowance is far above the real cost, the excess counts as pay and raises the overtime rate, so tie the allowance to the nights away from home rather than to the hours worked.

The UK equivalent: casual work, zero-hours and bank staff

Per diem is not a UK employment term. The same arrangement is called casual work or a zero-hours contract, and in the NHS and care sector the pool is the staff bank, with bank staff picking up shifts where a ward is short.

GOV.UK describes a zero-hours worker as on call when needed: the employer does not have to offer work, and the worker does not have to accept it. Someone in that position is usually a worker in law, which brings these rights:

• at least the National Minimum Wage for every hour worked

• statutory paid holiday, which builds up with the hours actually worked

• rest breaks and the 48-hour average week

• protection against unlawful deductions from pay and against discrimination, and no less favourable treatment for working part-time

Two points catch employers out. An exclusivity clause that stops a zero-hours worker taking work from another employer cannot be enforced, and the worker can simply ignore it. And for irregular-hours workers, employers may now pay holiday as rolled-up holiday pay on top of each period's wages, but only for leave years that began after 31 March 2024. What the Employment Rights Act 2025 changes for this group is covered in a separate article on zero-hours contracts and the new rules.

Per diem work for employers and for staff

For the employer, a per diem pool is cover that costs nothing in the weeks it is not used. Absences and peaks get filled without piling overtime on the regular team and without an agency margin. Roles that are only needed now and then, such as a night radiographer or extra bar staff for the wedding season, can be filled for exactly those hours.

The price is predictability. Per diem staff can say no, and the shifts everyone wants off, such as Christmas and summer weekends, are the ones they turn down most. A pool that is too small falls apart the first time two people go on holiday at once. Each new person also needs training and a few shifts before they work at the pace of the regular team, so a pool with high turnover costs more than it looks.

For the employee the picture is the other way round. They control their own schedule and often earn a higher hourly rate, against no guaranteed income, few or no benefits and shifts that can be cancelled at short notice. Many per diem staff combine it with a job elsewhere, or use it to stay in their profession while studying or after retiring.

Scheduling a per diem pool

A per diem pool only works if the people in it see open shifts quickly and can claim them without a round of phone calls. Ask everyone in the pool to keep their availability up to date, so before you post a shift you already know who is likely to take it. Post shifts as soon as the gap is known, to everyone qualified at the same time, and let the first to claim get it. That is faster than working down a list, and nobody can say the manager has favourites.

Write down the rules for minimum shifts and cancellations and apply them the same way to everyone. Keep an eye on the hours per person as well: in the US the 40-hour week and the 30-hour average are the lines to watch, in the UK the 48-hour average and the holiday that builds up with every shift. Count the clocked hours rather than the planned ones.

In Shiftbase, per diem staff and the regular team sit on one schedule. Your team sets their availability in the mobile app, and when a gap opens you publish it as an open shift that people can claim in the app, so the shift is covered without ringing round. Because everything sits in one place for employee scheduling, contract hours, approved leave and availability are visible while you plan, and the hours worked are ready to export for payroll.