To calculate how much sleep you need, start with the guideline for your age (7 to 9 hours for adults 18 to 64, 7 to 8 hours from 65), then narrow it down with a no-alarm test: sleep without an alarm for a week or two and average the last few nights. That average, once the catch-up sleep of the first nights has faded, is a good estimate of your personal need.
The sleep needs by age calculator gives you the first part in seconds. The self-test below gives you the second.
Free toolSleep Needs by AgeRecommended hours for every age, from newborns to over-65s.Step 1: calculate your range by age
Your age sets the range your need most likely falls in. These are the ranges recommended for adults by US sleep experts; the American Academy of Sleep Medicine puts the adult minimum at 7 hours.
| Age | Recommended sleep | Bedtime window for a 6:30 AM alarm |
|---|---|---|
| 18 to 64 | 7 to 9 h | 9:15 PM to 11:15 PM |
| 65 and over | 7 to 8 h | 10:15 PM to 11:15 PM |
Each bedtime allows 15 minutes to fall asleep. For children and teens, the ranges are higher; the sleep needs by age calculator covers every age from newborn up.
A range of 2 hours is wide. Someone who needs 7 hours and someone who needs 9 will feel very different on the same schedule. That's where the self-test comes in.
Step 2: the no-alarm sleep need calculator
Your sleep need is roughly what you settle at when you can sleep as long as you like for several nights in a row. Researchers use the same idea in the lab. In one study, 15 healthy young men spent 12 hours in bed every night for 9 nights. Their sleep jumped at first, then tapered off to a steady level that averaged about 8.4 hours, around an hour more than they'd been getting at home.
You can run a home version during a vacation or any stretch without early commitments:
- Pick 7 to 14 days with no alarm and no early plans. Longer is better.
- Go to bed when you feel sleepy and don't set an alarm. Keep caffeine to the morning and skip alcohol, which both distort the result.
- Log how long you actually slept each night, not just time in bed. The hours of sleep calculator turns bedtime and wake time into hours.
- Ignore the first few nights. If you're carrying sleep debt, you'll sleep long at first. That's catch-up, not your need.
- Average the last 3 or 4 nights. That's your estimate.
Worked example: calculating your sleep need
Formula: sleep need ≈ average sleep over the final nights of the no-alarm period. Here's a real-numbers example from a one-week test.
| Night | Hours slept |
|---|---|
| 1 | 9.5 |
| 2 | 9.0 |
| 3 | 8.6 |
| 4 | 8.3 |
| 5 | 8.2 |
| 6 | 8.1 |
| 7 | 8.2 |
Nights 4 to 7 average 8.2 hours (8.3 + 8.2 + 8.1 + 8.2 = 32.8, divided by 4). Rounded to the nearest 15 minutes, that's 8 hours 15 minutes of sleep.
Now turn it into a bedtime: 6:30 AM alarm minus 8 hours 15 minutes minus 15 minutes to fall asleep = 10:00 PM.
You can also calculate your everyday shortfall. If you normally sleep 7 hours on work nights, you're about 1.2 hours short each night, or 6 hours over a five-day week. The sleep debt calculator tracks this for you, and how to calculate sleep debt explains the math.
That big first night is a clue too. In the lab study above, how much extra people slept on the first free night was a simple sign of how much sleep debt they were carrying.
No time for a vacation test? Quicker checks
If you can't take a week off, use daytime sleepiness as your gauge. You're probably getting enough if most of these are true on your usual schedule:
- You wake up close to your alarm, or before it, without feeling dragged out of bed.
- You get through the morning without needing caffeine to function.
- You don't nod off within minutes when you sit still in a warm room or a meeting.
- Your weekend sleep is no more than about an hour longer than your weeknight sleep.
If several are false, try adding 30 minutes a night for two weeks and see what changes. More signs are in signs you're sleep deprived.
Caveats: why the calculation isn't perfect
Any home estimate is approximate, and it can be thrown off in both directions.
- You may not feel short on sleep even when you are. In a well-known lab study, people limited to 6 hours a night for two weeks built up deficits similar to one or two nights of total sleep loss, yet rated themselves only slightly sleepy.
- Paying back debt takes time. In the extended-sleep study, it took days of long sleep opportunities before sleep settled, which is why a weekend isn't long enough for this test.
- Stress, a new bed, noise, alcohol or illness during your test week will skew the numbers.
- Needing much more than 9 hours regularly, or waking unrefreshed however long you sleep, is worth discussing with a doctor. So is loud snoring with gasping or pauses in breathing.
Once you have your number, the most useful thing to do with it is set a fixed wake-up time and count back to a bedtime. Enter both into the sleep needs by age calculator to check it against your age range.