First, know the basic rule: All work performed in excess of 40 hours in one week is considered overtime and must be paid at one and a half times (1.5x) your regular rate or pay. Let's say your pay is $15 an hour and you work 50 hours in one week, you should be paid $22.50 for any work performed over 40 hours in a week. Thus, you would be owed $600 in regular pay (40 hours x 15) and $225 in overtime pay (10 hours x $22.5).
California Labor Code §510 provides multiple ways for employees to earn overtime. In addition to the 40 hours rule noted above, employees who work more than eight hours in a workweek must be paid at the rate of one and one-half times their regular pay. Let's say your friend's regular pay is $25 an hour and, she works 11 hours in a single day, she should be paid $37.50 an hour (1.5x25) for any work she performs in excess of eight hours in a day. Thus, your friend would be owed $200 in regular pay (8 hours x $25) and $112.50 in overtime pay (3 hours x 37.50).
A lot of employees are not aware of the double pay for work in excess of 12 hours in one day. California Labor Code §510 also provides that an employer must pay an employee double (2x) if she or she works in excess of 12 hours in a single day. Furthermore, California labor statutes require that employees be provided at least one day's rest in seven consecutive days of work.
Keep in mind that not all employees are entitled to overtime, but many employees are under the misconception that just because they are salaried, they are not entitled to overtime. A series of tests will be applied in these circumstances, contacting an attorney would be the best option for an employee.
You should also know that the rules above do not apply to workers that are covered by a collective bargaining agreement (CBA) that already provides for: (1) premium rates for all overtime worked; (2) the wages, hours of work, and working conditions of the union workers; (3) a regular hourly rate of pay of not less than thirty percent more than the state minimum wage rate.
Don't let your employer intimidate you, know that you can request for a copy of your payroll records. And if you feel that you are entitled to overtime and have not received proper compensation, you might consider taking legal action against your employer. Finally, remember that any retaliation for asserting your right to be paid fair and lawful wages is illegal and may be grounds for a wrongful termination case.