The overtime formula
overtime rate = hourly rate × multiplier (1.5 or 2)
weekly pay = (rate × regular hours) + (overtime rate × OT hours)
The federal Fair Labor Standards Act (FLSA) sets the floor: at least 1.5× your regular rate for anything over 40 hours in a workweek. Your "regular rate" legally includes most non-discretionary bonuses and shift differentials, so if you earn those, your true overtime rate may be slightly higher than base × 1.5.
A worked example
At $20/hour with 8 overtime hours: regular pay is $20 × 40 = $800, the overtime rate is $30/hour, and overtime pay is $30 × 8 = $240 — a weekly total of $1,040. Those 8 extra hours raised the paycheck by 30%, which is why overtime-heavy weeks can push your withholding into a higher bracket temporarily (you get the difference back at tax time).
State rules worth knowing
A few states go beyond the federal weekly standard. California pays daily overtime after 8 hours in a day and double time after 12; Alaska, Nevada, and Colorado also have daily thresholds. If you work in one of those states, calculate per-day, not just per-week.