Overtime
Overtime may be paid at different rates, based on the industry and agreement. Generally, you should review your contract to know what you should expect. Overtime can be calculated also on different methods, here are some methods that could have your overtime explained:
Overtime Per Week
When your overtime and leave is calculated per week, then you would have to check overtime as the hours worked week by week. This means that you should not be comparing the hours worked in the month, but only compare the weekly one.
For a few employees, their payslip may include such a Weekly Hour Breakdown, as found in the screenshot below. In such breakdown, Buddy includes the dates of the weeks, the total hours worked or taken on leave, as well as the difference with the scheduled hours. Generally, any hours worked over will be paid as overtime, whereas the other hours may be handled differently, based on company policy
Since the last week is generally not finished and continues within the next month, therefore, you would have to compare your hours based on the weeks finished during this payroll, rather than the hours worked in the whole month.
Overtime Per Month
If your overtime is being calculated and averaged over the pay period (e.g. per month), then this might be easier to calculate.
Generally overtime will be the average of hours worked over the scheduled normal hours in the month (this can be compared either with the 173.33 or the exact scheduled hours), based on the employer's methodology. You can deduct your total hours with the target scheduled to find out your overtime due.