When does a part-time job become a full-time job?

While everyone uses the terms "full time" and "part time" in describing work, they don't really have any legal importance--that is, under the law, one does not get any more benefits for being full time than part.

Here are the rules:

1) If an hourly employee, he or she must be paid at his or rate for all hours worked, and be paid overtime if more than 40 hours are worked in a week, regardless of whether he or she is considered full or part time.

2) IF the company provides health benefits or other benefits (e.g. 401k matches), employees must get them if they work enough hours regardless of whether they are officially "full time" or not. The law does not require companies to provide benefits, or, if they do, specify the hours to qualify; that is based on whether the company wants to offer benefits and what contract/plan/etc. they have with their benefit providers. (For example: a company can set the eligibility criteria for health insurance; whatever threshhold it sets will be in the master contract with the insurer.) The only rule is that whatever criteria or hourly threshold is chosen, the company must apply that all employees.

3) Certain laws or government benefits (e.g. FMLA; elibigility for unempoyment insurance) require a certain minimum amount of hours to qualify. Whatever that minimum is, if an employee reaches it, he or she is eligible regardless of whether full or part time.

Getting back to point 2: companies don't need to provide benefits, and if they do, determine the rules for getting them. They just have to be even-handed in applying whatever rules or standard they settle on.