Calculate the best time to go to bed or wake up based on sleep cycles.
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How the Bedtime Calculator Works
A good night's sleep isn't just about how many hours you get, but rather completing full sleep cycles. Humans typically experience sleep in 90-minute cycles. If you wake up in the middle of a cycle—specifically during deep sleep—you are likely to feel groggy and tired (a phenomenon known as sleep inertia), regardless of how long you actually slept.
This calculator helps you time your sleep so that you wake up at the end of a cycle, making you feel more refreshed and alert. It also accounts for the average of 14 minutes it takes for a person to fall asleep.
The Importance of Sleep Cycles
Each 90-minute cycle consists of several stages: Light sleep, Deep sleep, and REM (Rapid Eye Movement) sleep. Waking up during the REM stage or the light sleep stage at the end of a cycle is ideal. For most adults, getting 5 or 6 cycles (7.5 to 9 hours) is the gold standard for optimal cognitive function and health.
Example Calculations
If you need to wake up at 7:00 AM, working backward through 90-minute cycles plus 14 minutes to fall asleep, your ideal bedtimes would be:
11:16 PM: For 5 cycles (7.5 hours of sleep).
9:46 PM: For 6 cycles (9 hours of sleep).
Conversely, if you go to bed at 11:00 PM, you should aim to wake up at 6:44 AM or 8:14 AM to ensure you aren't interrupted during deep sleep.
Tips for Better Sleep Quality
While timing is crucial, sleep hygiene also plays a major role. Ensure your room is dark and cool, avoid screens 30 minutes before bed, and try to maintain a consistent schedule, even on weekends. If you consistently struggle to fall asleep within the 14-minute window provided in our calculations, consider relaxation techniques like deep breathing or progressive muscle relaxation.
function formatTime(date) {
var hours = date.getHours();
var minutes = date.getMinutes();
var ampm = hours >= 12 ? 'PM' : 'AM';
hours = hours % 12;
hours = hours ? hours : 12;
minutes = minutes < 10 ? '0' + minutes : minutes;
return hours + ':' + minutes + ' ' + ampm;
}
function calculateBedtimes() {
var h = parseInt(document.getElementById('wakeHour').value);
var m = parseInt(document.getElementById('wakeMinute').value);
var ampm = document.getElementById('wakeAMPM').value;
if (ampm === "PM" && h < 12) h += 12;
if (ampm === "AM" && h === 12) h = 0;
var wakeTime = new Date();
wakeTime.setHours(h, m, 0, 0);
var resultsHtml = '
You should try to fall asleep at one of the following times:
';
// Cycles: 6, 5, 4
var cycles = [6, 5, 4];
for (var i = 0; i < cycles.length; i++) {
var sleepTime = new Date(wakeTime.getTime());
// Subtract 90 mins * cycle count + 14 mins to fall asleep
var totalMinutesBack = (cycles[i] * 90) + 14;
sleepTime.setMinutes(sleepTime.getMinutes() – totalMinutesBack);
var sleepAmountHours = (cycles[i] * 90) / 60;
resultsHtml += '
';
}
var resDiv = document.getElementById('sleepResults');
resDiv.innerHTML = resultsHtml;
resDiv.style.display = 'block';
}
function calculateWakeUpTimes() {
var now = new Date();
// Add 14 minutes to fall asleep
now.setMinutes(now.getMinutes() + 14);
var resultsHtml = '
If you go to bed now, try to wake up at:
';
// Suggesting 4, 5, and 6 cycles
var cycles = [4, 5, 6];
for (var i = 0; i < cycles.length; i++) {
var wakeTime = new Date(now.getTime());
wakeTime.setMinutes(wakeTime.getMinutes() + (cycles[i] * 90));
var sleepAmountHours = (cycles[i] * 90) / 60;
resultsHtml += '