Sleep Calculator

Find the best bedtime or wake-up time based on 90-minute sleep cycles. Free, instant, no signup.

How to use the Sleep Calculator

  1. Enter your values. Fill in the fields with your numbers.
  2. Calculate. Press Calculate to run the sleep calculator.
  3. Use the result. Copy the result or try a related tool next.

Why use our Sleep Calculator

Instant results. Enter your figures and the sleep calculator returns an answer in seconds.
Free & private. Runs in your browser — no signup, and nothing is sent to a server.
Accurate. Uses standard formulas so you can rely on the numbers.

Free to use — premium coming soon

FREE
  • Unlimited calculations
  • Instant results
  • No signup
PREMIUM
  • Remove ads
  • Save & compare scenarios
  • Export results

About the Sleep Calculator

The Sleep Calculator works out the best times to go to bed or wake up so that your alarm lands at the end of a sleep cycle rather than in the middle of one. Sleep runs in repeating cycles of roughly 90 minutes, and each cycle moves through light sleep, deep sleep, and REM. Waking at the natural seam between cycles tends to leave you feeling clear-headed, while being jolted awake mid-cycle, especially out of deep sleep, is what produces that heavy, groggy feeling. Enter either your wake-up time or your bedtime and the tool counts cycles in the right direction for you.

Reach for it the night before an early start, a flight, an exam, or a job interview, when you cannot get a full night but want the rest you do get to count. It is equally handy for fixing a drifting schedule: if you keep waking up exhausted despite eight hours in bed, your alarm may simply be falling in the wrong part of a cycle. Parents use it to plan a child's bedtime backward from the school run, and shift workers use it to map sleep around irregular hours. Because it suggests several options, you can pick the one that fits the time you actually have.

Under the hood the math is straightforward. The calculator takes your anchor time and adds an allowance for sleep latency, the time it takes to actually drift off after the lights go out, which averages around 14 minutes. It then steps in 90-minute blocks, counting backward from a wake time to find candidate bedtimes or forward from a bedtime to find good alarm times. Most adults do best with five or six cycles, which is why the tool highlights options around the 7.5 to 9 hour mark, while still showing the shorter four-cycle choice for nights when six hours is all you can manage.

Treat the results as well-reasoned estimates, not a clinical readout. Ninety minutes is a population average; real cycles vary from about 70 to 120 minutes and lengthen as the night goes on, so your perfect wake time may sit a little either side of the suggestion. Only a sleep study can measure your true cycles. On privacy: the calculator runs entirely in your browser using simple time arithmetic. Nothing you type is sent to a server, stored, or used to track you, so you can plan your sleep without leaving any trace behind.

Frequently asked questions

How long is one sleep cycle?

A full cycle averages about 90 minutes, though it can range from roughly 70 to 120 minutes. Cycles tend to be shortest early in the night and grow longer, with more REM sleep, toward morning.

Why do I feel more tired after eight hours than after six?

It is usually about timing, not total hours. If your alarm interrupts a deep-sleep phase mid-cycle you wake groggy, whereas waking at the end of a cycle, even after fewer hours, often feels more refreshing. The calculator aims your wake time at those cycle boundaries.

How many sleep cycles should I aim for?

Most adults feel best with five to six cycles a night, which is about 7.5 to 9 hours of sleep. Four cycles, around six hours, is a workable minimum on a short night, but it is not ideal as a routine.

Does the calculator account for time to fall asleep?

Yes. It adds a sleep-latency buffer of about 14 minutes, the average time people take to drop off, before it starts counting cycles. If you usually fall asleep faster or slower, shift the suggested bedtime accordingly.

Is this a substitute for advice about a sleep disorder?

No. It is a planning tool based on average cycle lengths, not a medical device. If you regularly struggle to fall asleep, stay asleep, or feel rested, speak to a doctor or a sleep specialist.

From our blog

How to Find Your Body Shape Accurately (and Why the Ratios Matter)

By the Super Simple Digital Tools Team · Updated June 2026

Most people guess their body shape from the mirror, but the mirror is a poor judge of proportion. A body type calculator removes the guesswork by turning three measurements into a clear ratio-based answer. The catch is simple: garbage in, garbage out. If your measurements are sloppy, the shape you get back will be wrong, sometimes by a whole category. Getting the inputs right is the single biggest factor in a useful result, so it is worth slowing down before you type anything in.

Start with the right tool, a flexible cloth or fibreglass tape rather than a stiff carpenter's tape. Stand relaxed in front of a mirror with your weight even on both feet. For the bust, wrap the tape around the fullest part while wearing a normal, well-fitted bra. For the waist, find the natural crease where your torso bends, usually just above the belly button, and avoid sucking in. For the hips, measure the widest point around the buttocks. Keep the tape level all the way around for each measurement.

Once you enter the three numbers, the calculator does straightforward arithmetic. It subtracts waist from bust, waist from hips, and bust from hips, then checks those gaps against fixed cut-offs. An hourglass shows a large waist gap with balanced bust and hips. A pear shows hips clearly winning. An apple, or inverted triangle, shows the bust winning. A rectangle shows all three close together. Because the system uses hard thresholds, a measurement that lands near a boundary can tip you from one shape into the next.

That sensitivity is exactly why you should measure twice and trust the average. If your first and second readings disagree by more than half an inch, take a third. Many people sit right between two shapes, often called a combination figure, and that is completely normal. If the calculator flips between, say, hourglass and pear on repeat tries, you simply carry traits of both, and you can borrow styling ideas from each category rather than forcing yourself into one.

Finally, treat the result as a map, not a verdict. Knowing your shape helps you predict how a cut will hang and gives you a vocabulary when talking to a tailor or filtering an online store. But the goal is clothes that make you feel good, not obedience to a chart. Use the proportions to balance a silhouette when you want to, and to deliberately break the rules when you would rather. The calculator gives you information; what you do with it is entirely your call.

  • Measure over thin clothing or bare skin, never over a bulky sweater, or your bust and hip numbers will read too large.
  • Take each measurement twice and average them, since a half-inch error near a threshold can change your shape category.
  • Don't hold your breath or pull the tape tight at the waist, measure relaxed for the number you actually live in.
  • If two shapes keep coming up, you have a combination figure, so pull styling ideas from both rather than picking one.

Read the full guide →

Tool by the Super Simple Digital Tools Team. Reviewed by our editorial team. Free to use, no signup required.

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