How to Calculate Work Hours Accurately (For Payroll and Freelancers)
Wage theft through payroll errors costs American workers an estimated $15 billion per year, according to the Economic Policy Institute. Most of it isn't malicious — it comes from rounding errors, miscalculated overtime, and imprecise time records. Whether you're an hourly employee verifying your paycheck or a freelancer invoicing clients, knowing exactly how to calculate work hours is one of the most valuable practical skills you can have.
The Basic Calculation: Hours Between Two Times
To find hours worked between a start time and end time, convert both to 24-hour format, subtract, and adjust for any breaks.
Example: you clock in at 8:45 AM and out at 5:30 PM, with a 30-minute unpaid lunch.
- 8:45 AM = 8.75 hours; 5:30 PM = 17.50 hours
- 17.50 − 8.75 = 8.75 hours gross
- Subtract 0.5 hours for lunch = 8.25 hours worked
The hours calculator handles this automatically, including overnight shifts that cross midnight.
Overnight Shifts and AM/PM Transitions
If you start at 10:00 PM and end at 6:30 AM, the naive subtraction gives a negative number. The correct approach: add 24 hours to the end time: 6:30 AM becomes 30:30 (decimal: 30.5). Subtract start: 30.5 − 22.0 = 8.5 hours.
Overtime Rules: What the Law Requires
In the United States, the Fair Labor Standards Act (FLSA) requires that non-exempt employees receive overtime pay at 1.5× their regular rate for all hours worked over 40 in a single workweek. The 40-hour threshold is per workweek, not per pay period. California adds daily overtime after 8 hours in a single workday.
Misunderstanding the workweek vs. pay period distinction is one of the most common sources of underpaid overtime. If you work 45 hours one week and 35 the next on a biweekly paycheck, you should receive 5 hours of overtime for week one — not zero because the two-week total is 80.
How Freelancers Should Track Time
- Track by project and client separately.
- Log in real time, not from memory. People consistently underestimate how long tasks take when reconstructing from memory at end of day.
- Include all billable activities. Emails, review calls, and revision rounds are potentially billable depending on your contract.
- Review weekly to spot scope creep early.
Use the hours calculator to independently verify your total hours for any pay period, then compare against your pay stub. Most states have a statute of limitations on wage claims of two to three years.