Sleep Calculator
Find the best times to wake up or go to sleep based on 90-minute sleep cycles to wake up feeling refreshed.
Did this tool work for you?
How to use this calculator
Waking between sleep cycles (rather than mid-cycle) dramatically reduces morning grogginess.
- 1
Enter the time you plan to go to bed (in 24-hour format, e.g. 23 for 11 PM).
- 2
Enter how many minutes it usually takes you to fall asleep (average is 14 minutes).
- 3
The calculator shows the ideal wake-up times aligned with the end of sleep cycles.
- 4
Wake up at one of the suggested times to feel most refreshed.
Frequently asked questions
How does the sleep calculator work out a wake-up time?
It converts your bedtime hour to minutes after midnight, adds the minutes you said it takes to fall asleep, then adds 4, 5 and 6 blocks of 90 minutes. The total is taken modulo 24 hours and shown on a 12-hour AM/PM clock. The five-cycle line is the highlighted one.
Why is the bedtime a whole hour only?
The field takes a number from 0 to 23 and the code reads only its whole-hour part, so 23.5 is treated as 23. To plan for a half-hour bedtime, enter the hour and add 30 to the minutes-to-fall-asleep box.
What happens with values outside 0 to 23?
The hour wraps around the clock: 24 is midnight, 25 is 1 am, and a negative value counts backwards from midnight. Minutes to fall asleep are rounded to a whole number, and a negative value is treated as 0.
Why does the page always say 7.5 to 9 hours?
That line is fixed text printed under every result and is not calculated from your entries. Individual sleep needs vary, so it should not override how rested you feel or advice from a health professional.
Why are only 4, 5 and 6 cycles shown?
Those are the three options coded in, equal to 6, 7.5 and 9 hours of sleep after you fall asleep. Shorter and longer nights are not listed. If you want to see three cycles, the separate wake up calculator on this site includes them.
Is the answer in my local time and does it know about daylight saving?
It is plain clock arithmetic with no time zone or date, so it does not know about daylight saving changes, travel across time zones or shift work. On a night when the clocks change, shift the result by the difference.
Can it tell me whether I am getting enough sleep?
No. It shows when 90-minute blocks would end, and nothing about sleep quality or health. If you wake unrefreshed regularly, or find it hard to fall asleep, speak to a doctor. This is general information, not medical advice.
Sleep calculator — wake-up times from your bedtime
The calculation in one line
Wake time equals bedtime plus time to fall asleep plus the number of cycles times 90 minutes. The bedtime is entered as an hour of the 24-hour clock, so 23 means 11 pm and 0 means midnight, and the fall-asleep allowance starts at 14 minutes and can be edited. The calculator reports the results for four, five and six cycles, which are 6, 7.5 and 9 hours of actual sleep, and marks the five-cycle line as the highlighted result.
Worked examples
Each case was run through the calculator and shows the wake times for four, five and six cycles.
| Bedtime | Fall asleep | 4 cycles (6 h) | 5 cycles (7.5 h) | 6 cycles (9 h) |
|---|---|---|---|---|
| 23 (11 pm) | 14 min | 5:14 AM | 6:44 AM | 8:14 AM |
| 22 (10 pm) | 30 min | 4:30 AM | 6:00 AM | 7:30 AM |
| 0 (midnight) | 14 min | 6:14 AM | 7:44 AM | 9:14 AM |
How the allowance for falling asleep shifts everything
Compare the first two rows. Going to bed an hour earlier would move every wake time an hour earlier on its own, but the second case also assumes 30 minutes to fall asleep instead of 14, which pushes the results 16 minutes later, so the five-cycle result lands at 6:00 AM, only 44 minutes earlier than the first case. The input is there for that reason: lying awake for 30 minutes uses up time that does not count as sleep. If your own habits fall somewhere else, replace the 14 with what you actually experience.
Inputs it will and will not interpret
The hour is reduced to a whole number and wrapped to a value between 0 and 23, so a typed 24 behaves as midnight. The minutes box is rounded and cannot go below zero. Beyond that there are no checks, and no date is involved: the results always refer to the next time that clock reading occurs after you fall asleep. Since the page uses only the numbers you supply, the answers are the same on a weekday and a weekend, in summer and in winter.
Treating the output as a guide
Ninety minutes is an average block length used for planning, not a measurement of your own sleep, and the tool has no way to detect when you actually drop off. The best use is to pick a consistent bedtime, note which suggested alarm time you tend to feel best at after a week or so, and keep that. If daytime tiredness, long delays falling asleep or frequent waking continue regardless of timing, a doctor is the right person to ask.
Learn more from an authoritative source:
CDCWake Up Calculator
Find the best times to wake up based on sleep cycles so you feel refreshed, not groggy.
Due Date Calculator
Calculate your estimated due date (EDD) and pregnancy milestones from your last menstrual period (LMP).
VO2 Max Calculator
Estimate your VO2 max (maximal oxygen uptake) from a 1.5-mile run time or a submaximal step test. Assess your aerobic fitness level.
One Rep Max Calculator
Estimate your 1RM (one repetition maximum) for any lift using weight and reps performed. Calculate training percentages for programming.
Running Pace Calculator
Calculate your running pace, finish time, or distance. Enter any two of the three values to find the third. Supports km and miles.
Waist-to-Hip Ratio Calculator
Calculate your waist-to-hip ratio (WHR) and assess your health risk category based on WHO guidelines. A key indicator of central obesity and metabolic risk.
Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →