Sleepwell

Sleep comes in cycles. Each one lasts about 90 minutes and moves through light sleep, deep sleep, and REM, the stage where you dream.

Timing is everything. Waking at the end of a cycle (rather than the middle) means you surface naturally, feeling clear-headed instead of foggy.

We do the math. Sleepwell counts backward (or forward) in 90-minute intervals, adding 15 minutes for the time it takes to fall asleep, so you can plan the perfect night.

What time should I go to bed if I need to wake up at 7am?

To wake up at 7:00 AM feeling refreshed, aim to go to bed at 9:45 PM (6 cycles), 11:15 PM (5 cycles), 12:45 AM (4 cycles), or 2:15 AM (3 cycles). These times account for the 15 minutes it takes to fall asleep and align with the natural end of a 90-minute sleep cycle.

How long is a sleep cycle?

A sleep cycle lasts approximately 90 minutes and moves through several stages: light sleep (NREM 1 and 2), deep sleep (NREM 3), and REM sleep. REM is the stage where most dreaming occurs and where memory consolidation and emotional processing happen. Most adults need 5 to 6 complete cycles per night, totalling 7.5 to 9 hours of sleep.

Why do I wake up tired even after 8 hours of sleep?

Waking up in the middle of a sleep cycle rather than at the end of one causes sleep inertia, the groggy, disoriented feeling that can last for hours. Even a full 8 hours of sleep can leave you feeling worse than 7.5 hours if your alarm interrupts a deep sleep or REM stage. Using a sleep cycle calculator helps you time your sleep so you wake naturally between cycles.

How many hours of sleep do I actually need?

Most adults need between 7 and 9 hours of sleep per night, which corresponds to 5 or 6 complete sleep cycles. Teenagers typically need 8 to 10 hours, while younger children need more. Quality matters as much as quantity: uninterrupted sleep that moves through full cycles is far more restorative than the same number of hours with frequent waking.

Does it matter what time I go to sleep, or just how long I sleep?

Both matter. Your body has an internal clock called the circadian rhythm that responds to light and darkness. Sleep that aligns with your natural circadian rhythm, typically between 10pm and 7am for most people, tends to be deeper and more restorative than sleep during the day. Night shift workers and people with irregular schedules often report poorer sleep quality even when they get enough total hours. The sweet spot is getting the right number of complete sleep cycles during a window that aligns with your body's natural rhythm.

Keep a consistent schedule. Going to bed and waking up at the same time every day, including weekends, regulates your circadian rhythm and makes it easier to fall asleep and wake up naturally.

Wind down before bed. The hour before sleep matters. Dim the lights, put the phone down, and give your nervous system a chance to shift into rest mode. Bright screens signal your brain that it's daytime.

Keep your room cool and dark. Your body temperature naturally drops during sleep. A cool room (around 65 to 68°F or 18 to 20°C) and complete darkness help trigger and maintain deeper sleep stages.

Avoid caffeine after 2pm. Caffeine has a half-life of about 5 to 6 hours, meaning half of a 3pm coffee is still in your system at 9pm. It disrupts deep sleep even when you feel like it has no effect on your ability to fall asleep.

Use your sleep cycles strategically. If you need to take a nap, keep it to 20 minutes (before entering deep sleep) or a full 90 minutes (one complete cycle). Waking in the middle of deep sleep during a nap leaves you feeling worse than before you lay down.

Watch what you eat before bed. Heavy meals within 2 to 3 hours of bedtime force your digestive system to work while your body is trying to rest, which can cause lighter, more disrupted sleep. If you need a late snack, stick to something light. Alcohol is deceptive too: it might help you fall asleep faster but it fragments your sleep in the second half of the night and suppresses REM sleep.

Sleepwell is a free sleep cycle calculator built to help you wake up feeling rested instead of groggy. The science behind it is simple: sleep happens in 90-minute cycles, and waking between cycles rather than in the middle of one makes a noticeable difference in how you feel. We built this tool because most existing sleep calculators are cluttered, hard to use, or buried behind ads and sign-up walls. Sleepwell is fast, free, and designed to be used right before bed, when you need an answer in seconds, not minutes. No account required, no data collected, no nonsense.