Sleep Cycle Calculator

Sleep cycles are commonly modeled around 80-100 minutes. Enter when you want to wake up (or when you are going to bed) and this calculator gives you four candidate times using a 90-minute cycle model plus an adjustable fall-asleep buffer.

Examples

Wake at 07:00

You want to wake at 7am. The 5-cycle (7.5h) bedtime is 23:16 once you allow ~14 minutes to fall asleep.

I know when I want to…: Wake up
Time format: 24-hour
Target time: 7:00 AM
Time to fall asleep: 14 min

Bedtime · 5 cycles · 7.5h (in range)

23:16

Bedtime · 6 cycles · 9h

21:46

Bedtime · 4 cycles · 6h

00:46

Bedtime · 3 cycles · 4.5h

02:16

Embed this calculator

Copy a free iframe snippet for articles, learning pages, forums, wikis, newsletters, and internal docs.

How It Works

Formula

t_{\text{out}} = t_{\text{in}} \pm (90 n + f) \pmod{1440}

Variables, symbols and units

$t_{\text{in}}$: The time you entered (wake-up or bedtime)
$t_{\text{out}}$: A candidate bedtime (or wake-up)
$n$: Number of full sleep cycles (3, 4, 5, or 6)
$f$: Time to fall asleep
$\pm$: Subtract for "I know my wake time"; add for "I know my bedtime"

Calculation method explained

Subtract (or add) multiples of 90 minutes plus your fall-asleep buffer from the time you provided. Four results map to 3, 4, 5, and 6 modeled cycles — 4.5h, 6h, 7.5h, and 9h. The 5-cycle option (7.5h) is highlighted because it is within the adult 7-9 hour range.

Sleep is modeled as a chain of 90-minute cycles. To find candidate bedtimes from a known wake-up time:

Convert the target time to minutes-since-midnight.
Subtract $90 n + f$ for $n \in \{3, 4, 5, 6\}$ — that's 4.5h, 6h, 7.5h, and 9h of sleep, plus your fall-asleep buffer $f$ .
Reduce modulo 1440 so a result before midnight wraps to the previous day.

From a known bedtime, the same arithmetic with addition gives candidate wake-up times. The 5-cycle (7.5h) result is highlighted because it falls within the adult 7-9 hour range.

References and source material

Examples

Wake at 07:00Wake up · 24-hour → 23:16

You want to wake at 7am. The 5-cycle (7.5h) bedtime is 23:16 once you allow ~14 minutes to fall asleep.

I know when I want to…: Wake up
Time format: 24-hour
Target time: 7:00 AM
Time to fall asleep: 14 min

Bedtime · 5 cycles · 7.5h (in range): 23:16

Going to bed at 23:00Go to bed · 24-hour → 06:44

You're in bed at 11pm. Five cycles puts your wake-up at 06:44.

I know when I want to…: Go to bed
Time format: 24-hour
Target time: 11:00 PM
Time to fall asleep: 14 min

Wake-up time · 5 cycles · 7.5h (in range): 06:44

Going to bed at 19:30Go to bed · 24-hour → 03:14

An early bedtime before a night shift. Wake-up options run from 00:14 (3 cycles) up to 04:44 (6 cycles).

I know when I want to…: Go to bed
Time format: 24-hour
Target time: 7:30 PM
Time to fall asleep: 14 min

Wake-up time · 5 cycles · 7.5h (in range): 03:14

Frequently Asked Questions

Why 90 minutes?

NHLBI describes sleep cycles as restarting every 80-100 minutes and repeating through the night. The calculator uses 90 minutes as a planning model, so treat the results as useful candidates rather than a stopwatch.

Is it better to wake mid-cycle or end-cycle?

This calculator aims for full-cycle timing because sleep stages repeat through the night. Treat the times as planning candidates; sleep quality, total sleep, and individual cycle length still matter.

How long does it take to fall asleep?

Use the field as a personal buffer between lights-out and sleep. The default is only a starting point; adjust it to match your own pattern.

Should I aim for 7.5 or 9 hours?

NHLBI guidance says most adults need 7-9 hours of sleep. The 5-cycle result is highlighted because it lands inside that range in this 90-minute model; the 6-cycle result lands at 9 hours.

What if I still wake up groggy?

Cycle timing helps, but it cannot cancel out sleep debt, alcohol, stress, illness, or conditions like sleep apnea. If you're lining up your wake-up time with a cycle and still feel wrecked most mornings, total sleep quality is probably the bigger issue.

Sleep Cycle Calculator

Wake at 07:00

How It Works

Examples

Frequently Asked Questions

Related Calculators

Water Intake Calculator

Heart Rate Zones Calculator

Calorie Calculator

All calculators