Age in Hours
Elapsed hours need an actual time
Age in Hours measures elapsed clock time between the two date-and-time values you provide and converts that interval into completed hours. Entering a real birth time makes the result much more meaningful than assuming midnight.
If the birth time is unknown, the page uses midnight as a placeholder, so the total can differ from the real value by almost a full day. Treat that result as an estimate rather than exact elapsed time.
Keep the time-zone assumption in view
The browser interprets both timestamps using its local time-zone rules. If the birth happened in a different time zone, convert the two moments to a common zone before treating the hour total as exact.
This is also why Age in Days and Age in Hours can tell slightly different stories around daylight-saving transitions: one counts calendar dates, while the other counts elapsed clock time.
Questions people ask
Do I need an exact birth time for this to be accurate?
Yes if you want the elapsed-hour total to be exact. Without it, the calculator assumes midnight, so the result can differ from the real total by almost a full day.