ClearBreathsWhat is the sleep calculator?
Sleep runs in cycles of roughly 90 minutes, moving from light sleep into deep sleep and dreaming and back again. Waking at the end of a cycle — in lighter sleep — feels far easier than being jolted awake mid-cycle. This calculator plans your night around 5–6 full cycles (about 7.5–9 hours) plus the ~15 minutes most people take to fall asleep.
Enter the time you need to wake up and it shows the best bedtimes; enter a bedtime and it shows the best times to set your alarm. Use the option that fits — and remember the cycle length is an average, so treat the times as a helpful target, not a stopwatch.
How to use it
- Choose whether you’re planning a bedtime (you know your alarm) or a wake time (you know when you’ll sleep).
- Enter the time you know — the calculator allows ~15 minutes to fall asleep.
- Pick one of the suggested times: the highlighted ones give you 5–6 complete cycles.
- Keep the time consistent night to night so your body clock locks in.
- Wind down for the last 30 minutes — dim lights, screens away, and a few slow exhales.
Why people use it
- Wake between cycles so you feel rested, not groggy
- Takes the guesswork out of what time to go to bed
- Helps you keep a consistent, body-clock-friendly schedule
- Plans in the time it actually takes you to fall asleep
Want a plan built around your moment?
These free tools are a great start. For a breathing plan matched to your goal — sleep, calm, focus, or energy — with guided classes and a calm voice that paces every breath, try one guided breath first.
Try one guided breath first Free to start · no credit card before your first resetFrequently asked questions
How does a sleep cycle calculator work?
It counts in 90-minute blocks — one full sleep cycle — and adds about 15 minutes for falling asleep. From your wake-up time it counts backwards to suggest bedtimes that land you at the end of a cycle; from your bedtime it counts forwards to suggest wake times.
How many hours of sleep do I need?
Most adults need 7–9 hours, which is 5–6 sleep cycles. Teenagers and children need more. Aim for the number of cycles that lets you wake naturally without an alarm on a free day.
Why do I wake up groggy even after 8 hours?
You were probably woken in the middle of a deep sleep cycle. Setting your alarm to land at the end of a cycle — what this calculator suggests — usually feels much easier, even with the same total hours.
Is the 90-minute cycle exact?
No — it’s an average. Real cycles vary from about 70 to 120 minutes and change through the night. Use the suggested times as a target and adjust by 10–15 minutes based on how you actually feel.
What helps me fall asleep faster once I’m in bed?
A longer exhale than inhale tells your nervous system it’s safe to switch off. Try 4-7-8 breathing or a simple inhale-4, exhale-6 for a few minutes after lights out.