Semi-monthly payroll means employees are paid twice each month, usually on fixed dates such as the 15th and the last day of the month, resulting in 24 pay periods per year.
In contrast, biweekly payroll pays employees every two weeks, typically on the same weekday (like every other Friday), which results in 26 pay periods per year. The key difference is that semi-monthly follows specific calendar dates, while biweekly follows a 14-day schedule.