How this calculator works
The reading is turned into seconds after midnight, the delta is added, and the total is split into whole days and a remainder inside one day. A positive day offset means the new time is that many days later; a negative offset means it fell back into an earlier day. Every day is treated as exactly 86400 seconds, with no leap seconds and no date attached.
Formula
T = 3600h + 60m + s + delta_seconds. day_offset = floor(T / 86400), and the remainder R = T - 86400 x day_offset lies from 0 to 86399. The new clock is floor(R/3600) hours, floor((R mod 3600)/60) minutes and R mod 60 seconds.
Worked example
23:30:00 plus 7200 seconds is 01:30:00 with a day offset of 1. 00:15:00 minus 1800 seconds is 23:45:00 with a day offset of -1.
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Frequently asked questions
Does this know about daylight saving time?
No. It is abstract clock arithmetic on 24-hour days. For real instants that cross a clock change, use the time-duration calculator, which takes explicit UTC offsets.
What does a day offset of 2 mean?
The result clock belongs to a reading two days after the original one. Only the time of day is shown, so the offset carries the missing date information.
Can the time be exactly 24:00:00?
No. Midnight is written 00:00:00 with a day offset of 1 when a positive shift reaches it. The input 24:00:00 is rejected as an invalid clock reading.