Sleep calculator / Planning guides

Bedtime calculator: choose when to go to bed

A bedtime calculator works backward from the time you need to wake up. Start with your alarm, subtract your sleep target, then subtract the time you usually take to fall asleep. The result is when to get into bed, rather than when you should already be asleep.

The bedtime formula

Bedtime = wake-up time − sleep duration − fall-asleep allowance.

For example, an eight-hour sleep target before a 6 AM alarm, plus 15 minutes to fall asleep, gives a 9:45 PM bedtime the previous evening. The same assumptions give 10:45 PM for a 7 AM alarm and 11:45 PM for an 8 AM alarm.

These examples assume no time awake during the night. If your sleep is interrupted, actual sleep can be shorter than the plan. Leave enough opportunity for rest and use your own observations to refine the schedule.

Start with the commitment you cannot move

Work, school, caregiving or travel may fix your morning alarm. In that case, choose the alarm first. Moving bedtime later without moving the alarm reduces your sleep opportunity. If neither time is flexible, simplify your evening routine where possible instead of treating a shorter cycle estimate as a solution.

Make an earlier bedtime achievable

Separate wind-down time from the fall-asleep allowance. If you need to get into bed at 9:45 PM, starting your entire evening routine at that moment will delay the plan. Prepare for the morning earlier and choose a bedtime you can follow consistently. A schedule that looks perfect on paper still needs to fit real life.

Compare common morning alarms

Use the 6 AM bedtime plan, 7 AM calculator page or 8 AM bedtime plan for duration tables and cycle comparisons. The detailed 7 AM article covers building a routine around that alarm.

Personalize the estimate

Open the bedtime calculator and change the alarm or fall-asleep allowance. Cycle suggestions are estimates; you can also plan directly around a duration target. Read sleep duration to understand the difference.

Source: NHLBI: how much sleep is enough.

Snoozely is a planning tool for adults. Set a separate alarm. If sleep problems or excessive daytime sleepiness persist, talk to a healthcare professional.