Time Calculator

Time is counted in base 60, so ordinary decimal addition breaks as soon as minutes pass 59. Adding 2 hours 45 minutes to 1 hour 30 minutes gives 3 hours 75 minutes, which the calculator carries into 4 hours 15 minutes. Typing 2.45 + 1.30 into a phone calculator gives 3.75, which is wrong twice: the inputs were not decimal hours, and neither is the output.

1. Enter each duration in its own row. Days, hours, minutes and seconds can be mixed, and decimals such as 1.5 hours are accepted.
2. Choose Add or Subtract for every row after the first. This handles a total such as a 3-hour flight plus a 1:50 layover minus a 25-minute delay credit.
3. Read the total three ways. The result shows days, hours, minutes and seconds, the same span as h:mm:ss, and decimal hours for billing or payroll.

Internally every value is converted to whole seconds, summed, then split back into units, so a long list of rows never accumulates rounding drift.

The third tab adds or subtracts a duration from a time of day and reports the new clock time in both 12-hour and 24-hour form, plus how many days forward or back it landed. Starting a 7 hour 45 minute drive at 9:00 AM puts arrival at 4:45 PM the same day. A 5 hour 30 minute task started at 9:00 PM ends at 2:30 AM, one day later. Subtracting 3 hours from 1:00 AM gives 10:00 PM on the previous day.

Useful cases include medication spacing, oven or slow-cooker timing, parking limits, shift handovers and working backward from a deadline. Enter the deadline, choose Subtract, and enter the time the job needs to find the latest start time.