Assuming your local time is the one shown in the reminder (8:21 AM), there are 15 hours and 39 minutes until 12:00 AM (midnight) of the coming day.

What 12 AM Means

  • 12 AM is the time commonly used to mark midnight, the start of a new calendar day.
  • On a 24‑hour clock, 12 AM corresponds to 00:00 at the beginning of the day.

How the time left is figured out

  • From 8:21 AM to 12:00 PM (noon) is 3 hours and 39 minutes.
  • From 12:00 PM to 12:00 AM (midnight) is 12 hours, so total time left is 333 hours 393939 minutes +++ 121212 hours === 15 hours and 39 minutes.

If your local time is different

  • The remaining time until 12 AM always depends on your current local clock time.
  • Online countdown tools let you enter your current time and target time (12:00 AM) to see the hours, minutes, and seconds left automatically.

Quick everyday uses

  • People often check “how long till 12 am” to time deadlines, game resets, sales launches, and day-change events like New Year’s.
  • Many sites and apps now embed live countdowns to midnight for events so users can track the exact remaining time easily.

TL;DR: From 8:21 AM, there are 15 hours 39 minutes until 12:00 AM (midnight) tonight.