The best bedtimes & wake-up times by sleep cycle — so you wake up refreshed, not groggy.
Your alarm / when you need to be up.
Adult average ~15 min. Cycles count from sleep onset.
Population average 90; real cycles ~80–120.
Labels which rows fall in your range — does not change the math.
Based on ~90-min sleep cycles + ~15 min to fall asleep. Waking at the end of a cycle (light sleep) helps you feel less groggy. These are estimates, not medical guidance.
Educational estimate, not medical advice. This tool schedules around the ~90-minute average sleep cycle plus the time it takes to fall asleep. It has no sensor and cannot detect your actual sleep stage — a wearable that tracks live stages will be more precise for any single night. Persistent grogginess, trouble falling or staying asleep, loud snoring, or daytime sleepiness warrant a conversation with a doctor or sleep specialist. All math runs in your browser.
The Sleep Calculator finds the best times to fall asleep (if you have a fixed wake-up time) or the best times to wake up (if you're going to bed now or at a set time). Sleep happens in roughly 90-minute cycles; waking at the end of a cycle — during lighter sleep — leaves you less groggy than waking mid-cycle. The tool counts cycles from when you're actually asleep, so it adds your fall-asleep time (about 15 minutes by default) before stacking cycles.
You need to wake at 7:00 AM, take about 15 minutes to fall asleep, and use the 90-minute cycle:
The 5- and 6-cycle options are highlighted as the sweet spot for adults (7.5–9 hours of actual sleep). Note the hours-of-sleep figure counts the cycles only — it excludes the fall-asleep time, because that's time in bed, not time asleep.
All clock math is done in integer minutes-since-midnight and wrapped with mod 1440
so midnight and overnight crossings never produce a negative or "tomorrow" error. In wake mode, each bedtime is
wakeMinutes − (cycles × cycleLength + latency). In bedtime mode, each wake time is
bedtimeMinutes + latency + cycles × cycleLength. Times are formatted to 12-hour clock only at the end
to avoid floating-point drift.
<iframe src="https://snaptoolsuite.com/sleep-calculator/?embed=1"
style="width:100%;max-width:560px;height:780px;border:0;"
title="Sleep Calculator" loading="lazy"></iframe>
<p>Free <a href="https://snaptoolsuite.com/sleep-calculator/">Sleep Calculator</a> by Snap Tool Suite</p>See it live: view a real embed example →
Wake at the end of a 90-minute cycle. For a 7:00 AM alarm, good bedtimes are about 9:45 PM (6 cycles, 9 h) or 11:15 PM (5 cycles, 7.5 h), counting ~15 min to fall asleep. The tool does the math for you.
About 90 minutes on average, but real cycles range ~80–120 min and lengthen across the night. It's a population average, not a measurement — adjust it in Advanced if you know your pattern.
Cycles only count once you're asleep. Skipping fall-asleep time (latency) is the #1 reason naive calculators are off by ~15 min, so this tool counts from sleep onset.
Most adults do well on 5–6 cycles (~7.5–9 h). The tool shows 4, 5, and 6 and highlights 5 and 6 as the sweet spot. Teens need more; 65+ a little less.
The rationale is well supported — grogginess is worst when woken from deep sleep, and a cycle ends in lighter sleep. But total sleep and quality matter too, and the tool has no sensor to read your real stage.
Yes. 100% free, everything runs in your browser. This is an educational estimate, not medical advice.
Everything is calculated in your browser. We don't store or sell your data. Educational estimate, not medical advice.