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Plan your sleep around your body clock

Restcalc calculates the perfect bedtime or wake-up time using natural 90-minute sleep cycles, so you rise during light sleep — refreshed, not groggy.

How sleep cycles work

Free sleep & bedtime tools

No signup. Works offline in your browser. Switch language anytime.

Bedtime Calculator

Enter the time you need to wake up. We count back in 90-minute sleep cycles plus ~15 minutes to fall asleep.

Times assume ~15 min to fall asleep. Earlier bedtimes give you more complete cycles.

Wake-up Calculator

Enter when you plan to go to bed. We add sleep cycles to find the best moments to wake up.

Waking at the end of a cycle means ending in light sleep — easier to get up.

Sleep Duration Checker

Enter your bedtime and wake time to see total sleep, completed cycles, and a quality rating.

Nap Calculator

Enter the current time to see the best window for a refreshing power nap or a full-cycle nap.

Keep naps before 3 PM and under 90 minutes to protect nighttime sleep.

Sleep Window Helper

Choose the time range you are free to sleep. We find the best bedtimes that complete full 90-minute cycles and wake you inside your window.

Assumes ~15 min to fall asleep. Best windows wake you at the end of your range; sleep earlier if you prefer.

Sleep Log & Trend

Log a few nights — just your bedtime, wake time, and how you felt. We turn it into a visual trend using the 90-minute cycle model.

DateBedtimeWakeFelt
Tip: fill from the most recent night back. Entries stay on this device only — nothing is uploaded.

Your sleep over time

Caffeine Cutoff Calculator

Enter your planned bedtime and sensitivity. We work back to your last safe cup.

A guideline, not medical advice. Caffeine half-life varies between people.

Bedtime Breathing Timer

Choose a rhythm, press start, and breathe with the circle. Inhale as it grows, exhale as it shrinks.

Ready
04:00

Slow breathing is a relaxation aid. If breath-holding makes you light-headed, anxious, or uncomfortable, stop.

How sleep cycles work

A good night is not just about hours — it is about timing.

Your brain moves through sleep cycles about every 90 minutes, alternating between light sleep, deep sleep, and REM (dream) sleep. A full night usually holds 4–6 cycles. Waking up between cycles — during light sleep — leaves you clear-headed; waking mid-deep-sleep is what causes grogginess. Restcalc simply works backwards from your alarm (or forwards from bedtime) to land you on a cycle boundary.

Science-backed sleep tips

Small habits, big difference.

Guides & articles

Short, practical explainers for each tool — read one, then try the calculator.

Bedtime Calculator
What time should you go to bed? Wake-up Calculator
When should you set the alarm? Sleep Duration
Are you getting enough cycles? Nap Calculator
How long should you nap? Sleep Window Helper
Best bedtime in your free hours Sleep Log
What a week of data tells you Sleep Checklist
Build a full-day wind-down Caffeine & Sleep
The half-life science Breathing for Sleep
Slow breath to wind down

Frequently asked questions

Everything you need to use Restcalc confidently.

Sleep products we recommend

Gear that helps you fall — and stay — asleep.

Restcalc is a participant in the Amazon Associates program. As an affiliate we may earn from qualifying purchases, at no extra cost to you. Links are marked “sponsored”.

About Restcalc