Time Calculator (Add & Subtract Hours)
Add or subtract time values — useful for calculating total hours worked, elapsed time between events, and scheduling calculations.
Time Calculation Guide
Adding and Subtracting Time
Time arithmetic works in base 60 (minutes and seconds), unlike everyday arithmetic in base 10. When adding minutes, if the result exceeds 59, carry 1 to hours. Example: 3 hours 45 minutes + 2 hours 35 minutes = 5 hours 80 minutes = 6 hours 20 minutes. When subtracting, borrow 60 from the hours if needed: 5 hours 10 minutes − 2 hours 45 minutes → borrow 1 hour: 4 hours 70 minutes − 2 hours 45 minutes = 2 hours 25 minutes.
Decimal Hours
Decimal hours (used in timesheets and invoicing) express time as a decimal fraction of an hour. 0.25 hours = 15 minutes, 0.5 hours = 30 minutes, 0.75 hours = 45 minutes. To convert h:mm to decimal: decimal = hours + minutes/60. To convert decimal to h:mm: hours = integer part, minutes = decimal part × 60. Example: 8.75 hours = 8 hours and 0.75 × 60 = 45 minutes = 8:45.
Timesheet Calculations
For weekly timesheet calculations: add up all daily hours then convert to decimal for invoicing. If your rate is £35/hour and you work 8 hours 45 minutes: convert to decimal (8.75 hours), multiply by rate = £306.25. If calculating overtime (time and a half after 37.5 hours): total hours in decimal, subtract 37.5 for regular hours, multiply remainder by 1.5, sum regular and overtime pay. Always confirm overtime threshold with your employment contract.
Time Zones and Date Arithmetic
Adding time across midnight rolls the day forward. Adding 6 hours to 22:00 gives 04:00 the next day. For scheduling across time zones, always work in UTC first, then convert to local time — this avoids daylight saving time ambiguities. Duration and elapsed time calculations can use simple subtraction when the times are the same day; overnight calculations require adding 24 hours if the end time is earlier than the start time.
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