BedtimeCalculation

Wake up refreshed, not groggy

Sleep in complete 90-minute cycles. Tell us when you want to wake up, and we'll tell you exactly when to go to bed.

Wake-up time
1
2
3
4
5
6
7
8
9
10
11
12
:
00
05
10
15
20
25
30
35
40
45
50
55
Advanced options

Why sleep cycles matter more than hours

A full night's rest isn't just about how long you sleep, it's about where in a sleep cycle you wake up. Each cycle lasts roughly 90 minutes and carries you through light sleep, deep sleep, and REM (dream) sleep. Wake at the end of a cycle and you'll rise feeling alert. Wake mid-cycle, especially during deep sleep, and even nine hours can leave you feeling like you've been hit by a truck.

How to use this calculator

  1. Pick a mode: choose your wake-up time, or tell us when you're going to bed (or hit "Sleep now").
  2. Get your times: we count in 90-minute cycles and add ~14 minutes for falling asleep.
  3. Aim for 5–6 cycles: that's 7.5–9 hours, the sweet spot for most adults.

Want more? Try the nap calculator, check your sleep debt, see how much sleep you need for your age, or take a quick sleep apnea risk test.

Frequently Asked Questions

How does the sleep calculator work?

Sleep happens in cycles of roughly 90 minutes, moving through light sleep, deep sleep, and REM. The calculator counts backward (or forward) in 90-minute cycles from your wake-up time or bedtime, and adds about 14 minutes for the average time it takes to fall asleep. Waking at the end of a cycle, instead of in the middle of deep sleep, helps you feel more refreshed.

How many sleep cycles do I need?

Most adults need 5–6 complete sleep cycles per night, which works out to 7.5–9 hours of sleep. 4 cycles (6 hours) can work occasionally, but consistently sleeping less than 5 cycles builds up sleep debt.

Why do I wake up groggy even after a long sleep?

If your alarm fires during deep sleep (stages 3–4 of a cycle), you experience 'sleep inertia', that heavy, disoriented feeling. Timing your wake-up to the end of a cycle, even with slightly less total sleep, usually feels much better.

How long does it take to fall asleep?

The average adult takes about 14 minutes to fall asleep, which is why the calculator adds this 'sleep onset' time automatically. If you know you take longer or shorter, adjust it in the Advanced options.

Are sleep cycles always exactly 90 minutes?

No, 90 minutes is an average. Cycles range from about 80 to 110 minutes and tend to get shorter with age (closer to 82 minutes for adults 55+). Enter your age in Advanced options and the calculator adjusts the cycle length for you.