Sleep Calculator

How much sleep you need at each age

Sleep need follows age more than anything else. The CDC sleep page, last reviewed in May 2024, lists a daily range for every age band, and the ranges are wide because individual need varies inside them.

One band needs a note. For adults 18 to 60 the CDC gives a floor of 7 hours and no ceiling. The National Heart, Lung, and Blood Institute puts the adult range at 7 to 9 hours. This calculator uses 7 to 9 for that band and treats 8 as the midpoint, which keeps the arithmetic honest for someone who wants a number to aim at rather than a floor to clear.

Worked example: a 23:15 bedtime and a 6:45 alarm

Lights out at 23:15 and the alarm at 6:45 puts 7 hours 30 minutes on the clock, which is 450 minutes. If falling asleep takes 20 minutes, the time asleep is 430 minutes, or 7 hours 10 minutes.

The adult target is 8 hours, so the night lands 50 minutes short of the midpoint. Over a week that is 5.8 hours of missing sleep, which is close to one full night. The night still clears the 7 hour CDC floor, so this is a schedule that works but does not build a reserve.

To hit the 8 hour target on the same alarm, lights out has to move to 22:25. That is the number the calculator prints at the bottom, and it is the one to put in a phone reminder.

Time in bed is not time asleep

Every hour you spend in bed is not an hour of sleep. The gap has a name, sleep efficiency, and it is the time asleep divided by the time in bed. In the example above it is 430 minutes divided by 450, or 95.6%.

Two things eat into it. The first is sleep latency, the minutes between lights out and sleep. A person who takes 20 minutes has a different schedule from one who takes 5, even with the same alarm. The second is waking during the night. The calculator only asks for latency, so if you wake for 30 minutes at 3 am, subtract it yourself: 7 hours 10 minutes becomes 6 hours 40 minutes, and the weekly gap grows to 9.3 hours.

Efficiency below about 85% is the point where the schedule stops being a scheduling problem. Lying awake for an hour or more on most nights, or waking and staying awake, is worth raising with a clinician rather than solving with a later alarm.

The weekly total is where a small gap shows up

A 50 minute shortfall is easy to dismiss on a Tuesday. Multiplied by seven it becomes 5.8 hours, and that is the number that explains a Friday afternoon. The calculator prints both for that reason.

The teen row is the one to look at twice. A 22:45 bedtime looks late only by adult standards, and for a 16 year old it still falls 10.5 hours short of the 9 hour target across a week. School start times are the usual reason, and the fix is an earlier lights out rather than a longer weekend lie-in.

Naps count toward the total, but only once

For children under 7, naps are part of the daily total, not a bonus on top of it. The preschool row above shows the arithmetic: 10 hours 10 minutes of night sleep plus a 60 minute nap is 11 hours 10 minutes, inside the 10 to 13 hour band.

For adults the picture is different. A short nap of 20 to 30 minutes can take the edge off a bad night, and it counts toward the 24 hour total the same way. What it does not do is repay a week of short nights in one sitting. A 90 minute nap on Saturday moves the weekly number by 1.5 hours and leaves the other 4.3 hours of the 5.8 hour gap untouched.

Long naps late in the day are the case to avoid. Sleep pressure builds while you are awake, and a two hour nap at 5 pm spends most of it before the night begins.

Shift work and split sleep

Night shifts and rotating schedules break the assumption that sleep happens in one block. The calculator still works, because it only cares about minutes asleep in 24 hours, but the inputs change: enter the main sleep block after the shift, then add any second block as nap minutes.

Take a nurse on 19:00 to 07:00 shifts who sleeps 08:00 to 13:30 with 25 minutes to fall asleep. That is 330 minutes in bed, 305 asleep, or 5 hours 5 minutes, and a second block of 90 minutes brings the day to 6 hours 35 minutes. Against an 8 hour target that is 1 hour 25 minutes short per day, and the fix is a longer main block rather than a third nap.

Split sleep works better when the two blocks are stable across the week. Rotating start times every few days are the part that hurts, because the body never settles into either schedule.

What the number cannot tell you

This calculator counts hours. It cannot measure sleep quality, and quality is the half of the picture that hours miss. The CDC lists trouble falling asleep, repeated waking and feeling tired after enough sleep as signs of poor quality.

The scale of the problem is measurable. In 2024, 30.5% of US adults slept less than 7 hours on average in a 24 hour period, according to NCHS Data Brief 559 from April 2026. That is roughly three in ten adults under the CDC floor, and it is the reason a weekly total is worth more attention than a single bad night.

Caffeine belongs in the same conversation. The half-life of caffeine in a typical adult is about 5 hours, per the NIH StatPearls review of caffeine, and the same review cites sleep hygiene guidance to avoid substantial caffeine at least 6 hours before bed. A 4 pm coffee still has a quarter of its dose in your system at 2 am.

None of this is a diagnosis. Snoring with pauses, gasping at night, or sleepiness that persists after 8 hours in bed are reasons to see a clinician, not to adjust a bedtime.