Sleep Calculator

Quick Answer

Last updated: 2 November 2026 ·How we calculate this: 90-minute sleep cycle average

How This Sleep Calculator Works

During the night, your body moves through repeating sleep cycles. This calculator uses a 90-minute average to suggest times that line up with the end of a cycle. It also adds the time you usually need to fall asleep.

How to Use the Sleep Calculator

1. Choose whether you want a bedtime or a wake-up time.
2. Enter the time you know: when you need to wake up, or when you plan to go to bed.
3. Enter how many minutes you usually take to fall asleep. 15 minutes is a common average.
4. Press Calculate to see times for 3 to 6 sleep cycles.
5. Pick the time that gives you at least 7 hours. The 5-cycle row is highlighted.

Core Formulas

• Sleep time: cycles × 90 minutes
• Bedtime: wake-up time − sleep time − minutes to fall asleep
• Wake-up time: bedtime + minutes to fall asleep + sleep time

Research describes cycles of roughly 90 to 110 minutes, and some sources say up to 120. The 90-minute figure is an average, so treat these times as a guide and not an exact rule.

Worked Example

You go to bed at 10:30 PM and take 15 minutes to fall asleep.

• Asleep at 10:45 PM
• 5 cycles = 7.5 hours, so wake at 6:15 AM
• 6 cycles = 9 hours, so wake at 7:45 AM

Real-Life Examples

• An early start: to wake at 5:30 AM after 5 cycles, with 15 minutes to fall asleep, go to bed at 9:45 PM.
• A late night: if you get to bed at 1:00 AM and need to be up for work, 4 cycles (6 hours) means waking at 7:15 AM. That is below the 7 hours adults need, so try to make up for it with an earlier night soon.
• A nap: one full cycle is about 90 minutes. Many people prefer a short nap of 20 to 30 minutes instead, which tends to leave you less groggy.
• Shift work: the calculator works for any time of day, so you can plan sleep after a night shift too.

Sleep Cycles vs Total Sleep

• Sleep cycles: waking at the end of a cycle may help you feel less groggy, but cycle length differs between people and nights.
• Total sleep: getting enough hours on a regular schedule has much stronger evidence behind it.
• Best use: use cycles to choose between bedtimes that already give you 7 or more hours.

Recommended Sleep by Age

CDC guidance for total sleep in 24 hours, including naps for young children.

Getting Better Sleep

• Keep a routine: going to bed and waking at similar times helps.
• Think about total sleep: the number of hours matters more than hitting an exact cycle.
• Age matters: children and teens need more sleep than adults.
• Get help if needed: speak to a doctor if you often feel tired or have trouble sleeping.

Common Mistakes to Avoid

• Forgetting time to fall asleep. Lying awake for 20 minutes shifts every cycle.
• Choosing too few cycles. 3 or 4 cycles is below 7 hours for most adults.
• Changing bedtime every night. A steady routine usually matters more than the exact minute.
• Relying on cycles alone. If you often feel tired after enough sleep, speak to a doctor.
• Late screens and caffeine. They can make it harder to fall asleep at the time you planned.

Frequently Asked Questions

References & Sources