How this calculator works
This forward planner adds time to fall asleep and the assumed sleep duration to bedtime. Cycle mode gives a table of alarm times for one through six assumed cycles; custom mode lets the first cycle differ from later ones. The chosen-duration mode is useful when you want an alarm based on hours rather than a cycle model. Labels distinguish a daytime wake time from one on the following day. The plan assumes uninterrupted sleep on a single local clock. NHLBI explains that cycles vary and that sleep stages are measured with physiological recordings, so an alarm time is not a prediction of a REM boundary. Short rows are arithmetic examples, not adequate-rest recommendations. The result is an estimate for information only and is not medical advice.
Formula
Wake time = bedtime + time to fall asleep + assumed time asleep. Cycle-based time asleep = first-cycle duration + (cycle count - 1) × later-cycle duration. Standard mode assumes 90 minutes for each cycle. Sleep plus latency must be less than 24 hours.
Worked example
Going to bed at 23:00, allowing 15 minutes to fall asleep and planning five 90-minute cycles gives a 06:45 alarm the next day. Six cycles instead gives 08:15. For daytime sleep starting at 07:00, 20 minutes to fall asleep and eight chosen hours gives 15:20 on the same day.
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Frequently asked questions
Can I calculate an alarm after daytime sleep?
Yes. Enter any 24-hour bedtime. The same-day or next-day label makes the date relationship explicit, including after a night shift.
Does the time to fall asleep add to sleep duration?
It adds to time in bed, not time asleep. If you expect eight hours asleep and need 20 minutes to fall asleep, the alarm is eight hours 20 minutes after bedtime.
Should I set an alarm from a predicted sleep stage?
This tool cannot predict a stage. Use the table to understand timing assumptions, and consider your sleep needs and obligations when choosing an alarm.