Calculate the best time to go to bed based on your biological needs and sleep cycles.
Adult (18-64 years)
Senior (65+ years)
Teen (14-17 years)
School Age (6-13 years)
Preschool (3-5 years)
Toddler (1-2 years)
Recommended Bedtimes
How Much Sleep Do You Really Need?
Sleep is not just a passive state of rest; it is a vital biological process where your body repairs tissues, synthesizes hormones, and consolidates memories. Most adults require 7 to 9 hours of quality sleep per night to function optimally. However, "how much sleep do I need" isn't just about the total hours; it's about the quality of the cycles.
The 90-Minute Sleep Cycle Rule
Human sleep occurs in cycles that last approximately 90 minutes. During these cycles, you move through light sleep, deep sleep, and REM (Rapid Eye Movement) sleep. Waking up in the middle of a deep sleep stage often results in "sleep inertia," leaving you feeling groggy and tired regardless of how many hours you slept. To wake up refreshed, it is best to complete 5 or 6 full sleep cycles.
Age Group
Recommended Sleep Hours
Newborns (0-3 months)
14-17 hours
Infants (4-11 months)
12-15 hours
Toddlers (1-2 years)
11-14 hours
Preschoolers (3-5 years)
10-13 hours
School-age children (6-13 years)
9-11 hours
Teens (14-17 years)
8-10 hours
Adults (18-64 years)
7-9 hours
Seniors (65+ years)
7-8 hours
Examples of Sleep Calculations
Example 1: The Standard Adult. If you need to wake up at 7:00 AM and want to get 7.5 hours of sleep (5 cycles), you should be asleep by 11:30 PM. If it takes you 15 minutes to fall asleep, you should get into bed at 11:15 PM.
Example 2: The Teenager. A 16-year-old needing 9 hours of sleep (6 cycles) who wakes up at 6:30 AM should be asleep by 9:30 PM.
Tips for Better Sleep Quality
Consistency: Go to bed and wake up at the same time every day, even on weekends.
Environment: Keep your bedroom dark, quiet, and cool (around 65°F or 18°C).
Blue Light: Avoid screens (phones, tablets, TVs) at least 60 minutes before bed as blue light inhibits melatonin production.
Caffeine: Limit caffeine intake in the afternoon and evening.
function calculateSleepTimes() {
var wakeTimeInput = document.getElementById("wakeTime").value;
var fallAsleepMinutes = parseInt(document.getElementById("fallAsleepTime").value) || 0;
var ageGroup = document.getElementById("ageGroup").value;
if (!wakeTimeInput) {
alert("Please enter a wake-up time.");
return;
}
var wakeParts = wakeTimeInput.split(":");
var wakeHour = parseInt(wakeParts[0]);
var wakeMin = parseInt(wakeParts[1]);
var bedtimeList = document.getElementById("bedtimeList");
var ageRecommendation = document.getElementById("ageRecommendation");
var resultArea = document.getElementById("sleepResultArea");
bedtimeList.innerHTML = "";
// Define sleep cycles (90 minutes each)
// We calculate for 6, 5, and 4 cycles (standard for adults)
var cycles = [6, 5, 4];
// Adjust cycles and message based on age
var ageText = "";
if (ageGroup === "adult") {
ageText = "Adults typically need 7-9 hours of sleep.";
} else if (ageGroup === "senior") {
ageText = "Seniors typically need 7-8 hours of sleep.";
cycles = [5.5, 5, 4.5]; // Slightly different for seniors
} else if (ageGroup === "teen") {
ageText = "Teens need 8-10 hours of sleep for healthy growth.";
cycles = [7, 6, 5];
} else if (ageGroup === "school") {
ageText = "School-age children need 9-11 hours of sleep.";
cycles = [8, 7, 6];
} else if (ageGroup === "preschool" || ageGroup === "toddler") {
ageText = "Young children need 10-14 hours of sleep including naps.";
cycles = [9, 8, 7];
}
ageRecommendation.innerText = ageText;
for (var i = 0; i < cycles.length; i++) {
var cycleCount = cycles[i];
var totalMinutesBack = (cycleCount * 90) + fallAsleepMinutes;
var wakeDate = new Date();
wakeDate.setHours(wakeHour, wakeMin, 0, 0);
var bedtimeDate = new Date(wakeDate.getTime() – (totalMinutesBack * 60000));
var timeString = bedtimeDate.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
var durationHours = (cycleCount * 90) / 60;
var div = document.createElement("div");
div.className = "bedtime-option";
div.innerHTML = "" + timeString + "" +
"" + durationHours + " hours sleep " + cycleCount + " cycles";
bedtimeList.appendChild(div);
}
resultArea.style.display = "block";
resultArea.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}