How this calculator works
Every duration is converted to whole seconds with 60 minutes to an hour and 60 seconds to a minute. The seconds are added as ordinary numbers, then split back into hours, minutes and seconds. Because the total is not wrapped at 24 hours, a sum of 30 hours stays 30:00:00 rather than becoming 06:00:00 on the next day.
Formula
For an entry written H:MM:SS, seconds = 3600H + 60M + S. The entries are summed: T = S1 + S2 + ... + Sn. The total text is floor(T/3600) hours, floor((T mod 3600)/60) minutes and T mod 60 seconds. Decimal hours = T/3600 and total minutes = T/60.
Worked example
Adding 2:45, 1:30 and 0:20 gives 4:35:00. In decimal form that is 4.583333 hours, 275 minutes or 16500 seconds. The running-total column shows 2:45:00, then 4:15:00, then 4:35:00.
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Frequently asked questions
How do I add a duration longer than 24 hours?
Just write it with the full hour count, for example 30:15 for 30 hours 15 minutes. The total is never wrapped at midnight, so it keeps counting upward.
Can I mix entry formats?
Yes. Each entry is read on its own, so 2:45, 1:30:15 and 0:20 can sit in the same list. A bare number without a colon is rejected because it could mean hours or minutes.
Are these calendar days or fixed 24-hour days?
They are fixed 24-hour days with no dates, time zones or daylight-saving changes. That is the right model for summing work durations and the wrong model for measuring the gap between two dated events.
What is the largest total I can enter?
There is no practical limit beyond the text length. Hours are read as an ordinary integer, so a single entry can be hundreds of hours long.