How to Add and Subtract Hours and Convert to Decimal Format
Calculating hours, minutes, and seconds is fundamentally different from base-10 mathematics because time relies on the sexagesimal numeral system (base 60) for minutes and seconds, and base 24 for daily hours.
How to Sum or Subtract Time with Day Shifts
When you add 00:05:02 to 08:36:00, the operation combines each component: 8 hours + 0 = 8h, 36 min + 5 min = 41 min, and 0 s + 2 s = 02 s, resulting in 08:41:02 on the same day. However, if you add 06:00:00 to 21:30:00, the sum totals 27:30:00, which wraps past midnight (24 hours) into 03:30:00 on the next day (+1 day).
Converting Sexagesimal Time to Decimal Hours
In payroll, invoicing, and freelance billing, hours must be entered as decimal numbers:
Decimal Hours = Hours + (Minutes / 60) + (Seconds / 3600)
For example, 7 hours and 45 minutes equals 7 + (45 / 60) = 7.75 hours.