Calculation Methodology & Math Rules
Full transparency into our mathematical models, rounding standards, annualization constants, and overtime logic.
1. Decimal Precision & Rounding Rules
To prevent floating-point calculation drift (such as JavaScript $99.999999999 errors), all calculations follow a strict multi-stage rule:
- Unrounded Intermediate Computation: Intermediate math operations (such as converting minutes to fractional hours) maintain full IEEE 754 double precision without early rounding.
- Standard Currency Rounding: Final currency amounts are rounded to two decimal places using standard half-up arithmetic rounding (e.g., $0.005 rounds up to $0.01).
- Decimal Hours: Converted hours are rounded to two decimal places (hundredths of an hour) matching standard payroll timesheet systems.
2. Shift Durations & Overnight Midnight Handling
Clock times are converted internally into total minutes from midnight (0 to 1,439 minutes).
This ensures that night shifts beginning at 10:00 PM (22:00) and ending at 6:30 AM (06:30) are accurately calculated as 8 hours and 30 minutes elapsed without requiring the user to manually enter dates.
3. Salary Annualization Constants
Standard full-time employment conversion benchmarks:
4. Overtime & Labor Multiplier Assumptions
In our overtime and time card calculators:
- Standard Overtime: Regular hourly rate × 1.5 for hours exceeding the user-specified weekly threshold (default 40.0 hours).
- Double-Time: Regular hourly rate × 2.0.
- Statutory Disclaimers: These are mathematical models. Overtime qualification (exempt vs. non-exempt status under the FLSA or local state law) is determined by job duties, salary basis, and jurisdiction.
5. Freelance Rate Formulation
This accounts for the reality that self-employed contractors must absorb both employer and employee portions of FICA taxes, pay for their own insurance, and spend time on unpaid administrative tasks.