Sleep calculator
Your night runs in roughly 90-minute cycles, and waking at the end of one feels far better than waking in the middle. Enter when you need to wake up, or when you're heading to bed, and we'll find the times that line up with a full cycle.
How sleep cycles work
When you sleep, your brain moves through repeating cycles of light sleep, deep sleep, and REM sleep, the stage where dreaming is most vivid. Each full cycle takes about 90 minutes, and a typical night strings together four to six of them. The trick to waking up clear-headed isn't only how long you sleep, but where in the cycle your alarm lands.
Wake up at the end of a cycle, while you're in lighter sleep, and getting up feels natural. Get pulled out of deep sleep in the middle of a cycle, and you can feel groggy for a while even after a long night. That heavy, foggy feeling is called sleep inertia, and it's exactly what this calculator is designed to help you avoid.
The times here are based on averages, so use them as a friendly guide. Add about 15 minutes to fall asleep, aim for 5 to 6 full cycles, and keep a steady schedule when you can, that consistency does as much for your rest as any single perfect bedtime.
Curious what happens once you drift off? Read our guide to REM sleep and why you dream, learn about lucid dreaming, or look up what last night's dream might mean in the dream dictionary.
Frequently asked questions
›How does the sleep calculator work?
It counts backward or forward in 90-minute sleep cycles and adds about 15 minutes to fall asleep. Waking at the end of a cycle, rather than in the middle of deep sleep, tends to leave you feeling more refreshed. Enter a wake-up time to get ideal bedtimes, or a bedtime to get ideal wake-up times.
›What is a sleep cycle?
A sleep cycle is one full loop through the stages of sleep, from light sleep into deep sleep and then into REM, where most vivid dreaming happens. Each cycle lasts roughly 90 minutes, and a healthy night usually includes four to six of them.
›How many hours of sleep do I need?
Most adults do best with 7 to 9 hours, which works out to about 5 or 6 full sleep cycles. Teenagers generally need more, and needs shift with age, health, and how hard your days are. The calculator highlights 5 and 6 cycles as the sweet spot for most people.
›Why do I wake up tired even after 8 hours?
Often it's because your alarm went off in the middle of a deep-sleep stage rather than at the end of a cycle. Waking mid-cycle can leave you groggy even after plenty of hours, an effect called sleep inertia. Aligning your alarm with the end of a cycle can help you feel clearer.
›Is it better to wake up at the end of a sleep cycle?
Generally, yes. Waking as a cycle finishes, when you're naturally in lighter sleep, tends to feel easier than being pulled out of deep sleep. The cycles are averages, not exact for everyone, so treat the times as a helpful guide rather than a strict rule.