Calculate the best time to wake up or go to sleep based on natural 90-minute sleep cycles. Wake up refreshed and avoid morning grogginess.
Time your alarm, or your bedtime, to land on the end of a 90-minute sleep cycle so you wake during light sleep instead of deep sleep. Enter a wake-up time, a bedtime, or tap Sleep Now, and the calculator maps every optimal window, adds a fall-asleep buffer, and even sizes your naps.
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Sleep runs in roughly 90-minute cycles that move from light sleep into deep sleep and finally REM. Waking in the middle of a cycle, especially during deep sleep, triggers sleep inertia, the groggy fog that lingers for up to 30 minutes. The calculator counts backward (or forward) in 90-minute blocks from your target time and adds a fall-asleep buffer, so each suggested time lands at the end of a cycle when you're already in light sleep and easiest to wake.
Choose “Wake up at”, “Sleep at”, or “Sleep now” depending on whether you know your alarm time, your planned bedtime, or want to go to bed immediately.
Enter the time you must wake up or plan to fall asleep. Sleep Now reads the current clock automatically and adds your fall-asleep buffer.
Each card shows a time that completes 3-6 full 90-minute cycles. The 5-cycle (~7.5 hour) option is highlighted as recommended for most adults.
Open Fine-tune to adjust your fall-asleep latency and average cycle length if you track your own sleep data with a wearable.
Use the nap calculator for a 20-minute power nap or a full-cycle recovery nap, both timed from the current moment.
Working an early shift? Use Wake-up mode to see the latest bedtimes that still deliver whole cycles. Heading to bed now? Sleep Now maps your best wake-up times from the current minute. The built-in nap calculator handles the two naps that actually work, a 20-minute power nap that boosts alertness without grogginess, and a single full-cycle recovery nap that includes REM. Everything is calculated locally in your browser, and the fall-asleep latency and cycle length are adjustable if your own data differs from the 90-minute average.
To wake up at 6:00 AM feeling refreshed, you should go to sleep at 8:45 PM (5 cycles), 10:15 PM (4 cycles), or 11:45 PM (3 cycles). The calculator adds 15 minutes for falling asleep.
Most adults need 7-9 hours (5-6 full sleep cycles). Teenagers need 8-10 hours. Children need 9-11 hours. Sleeping less than 6 hours (4 cycles) consistently creates sleep debt.
A sleep cycle lasts approximately 90 minutes and includes light sleep, deep sleep (slow-wave), and REM sleep. Most people complete 4-6 cycles per night. Waking between cycles reduces grogginess.
This is called sleep inertia, it occurs when an alarm wakes you during deep sleep. Our calculator times your wake-up to coincide with the end of a 90-minute cycle, so you wake during lighter sleep stages.
REM sleep is most abundant in the later sleep cycles (cycles 4-6, roughly 5-9 hours into sleep). Going to bed before midnight maximizes total REM sleep time and memory consolidation.
For most adults, 6 hours is not enough long-term. Studies show it impairs cognitive function similarly to being awake for 24 hours. The minimum for healthy adults is 7 hours (4.5 cycles).
Sleep runs in ~90-minute cycles, so you feel best waking at the end of one. To wake at 6:00 am, good bedtimes are about 9:00 or 10:30 pm (5-6 cycles), plus ~15 minutes to fall asleep. Enter your wake time to get the exact bedtimes.
Enter the current time and the calculator lists wake times that fall at the end of complete 90-minute cycles, so you wake refreshed rather than mid-cycle and groggy.
Most adults need 5-6 cycles (about 7.5-9 hours). The calculator counts back in 90-minute cycles from your target so you land on a full cycle.
You likely woke in the middle of a deep-sleep cycle. Waking at the end of a 90-minute cycle, even with slightly less total sleep, usually feels more refreshing.
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