Fitness & Health

Sleep Calculator

Find optimal bedtime and wake time by sleep cycles.

Inputs

Adjust the assumptions to match your scenario. Results update instantly.

Wake time (hour, 0-23)Desired wake-up hour in 24-hour format.Sleep cycle (minutes)Length of one sleep cycle (typically 90 minutes).Time to fall asleep (min)Average minutes needed to fall asleep.

Results

Primary outputs and comparison insights are built from the current inputs.

Bedtime (6 cycles)

21.75

Bedtime for 6 full sleep cycles (~9 hours).

Bedtime (5 cycles)

23.25

Bedtime for 5 full sleep cycles (~7.5 hours).

Bedtime (4 cycles)

0.75

Bedtime for 4 full sleep cycles (~6 hours).

How this calculator works

The Sleep Calculator suggests ideal bedtimes based on complete 90-minute sleep cycles so you wake between cycles and feel rested. Enter wake time (hour, 0-23), sleep cycle (minutes), and time to fall asleep (min) to estimate bedtime (6 cycles), bedtime (5 cycles), and bedtime (4 cycles). The calculator updates instantly and adds a comparison table plus chart so you can test the sensitivity of the result before you use it in a decision.

Quick guide

Jump straight to the section you need, then return to the calculator.

Inputs Outputs Assumptions Tips Formulas Examples Reference table Visual breakdown References

Inputs

Desired wake-up hour in 24-hour format.
Length of one sleep cycle (typically 90 minutes).
Average minutes needed to fall asleep.

Outputs

Bedtime for 6 full sleep cycles (~9 hours).
Bedtime for 5 full sleep cycles (~7.5 hours).
Bedtime for 4 full sleep cycles (~6 hours).

Assumptions

Average sleep cycle is 90 minutes.
Waking between cycles reduces grogginess.

Tips

Most adults need 5-6 cycles (7.5-9 hours).
Keep a consistent schedule even on weekends.

Formula guide

Use these formulas to audit the output or explain it to someone else.

1 formulas

Bedtime = Wake Time − (Cycles × Cycle Length) − Fall Asleep Time

Usage examples

Review a ready-made scenario, copy it, then tweak inputs to match your case.

Example

3 inputs3 outputs

Early riser plan

Inputs

Example input Wake time (hour, 0-23): 6
Example input Sleep cycle (minutes): 90
Example input Time to fall asleep (min): 15

Outputs

Example result Bedtime (6 cycles): 20.75
Example result Bedtime (5 cycles): 22.25
Example result Bedtime (4 cycles): 23.75

For a 6 AM wake time, going to bed at 9:15 PM or 10:45 PM completes full cycles.

Bedtime by wake time

5 of 5 rows

Wake time (hour, 0-23)	Bedtime (5 cycles)	Bedtime (6 cycles)
5	21.25	19.75
6	22.25	20.75
7	23.25	21.75
8	0.25	22.75
9	1.25	23.75

Waking between sleep cycles leads to feeling more refreshed.

Bedtime suggestions

Highest: 7 (23.25)Lowest: 8 (0.25)

Sort

Wake time (hour, 0-23)Bedtime (5 cycles)

Focus point

21.25

Position

#1 of 5

Original order

Share of total

31.14%

Total: 68.25

PositiveNegative

Waking between sleep cycles leads to feeling more refreshed.

References

Sleep cycle duration research
National Sleep Foundation recommendations

FAQ

Common questions

What does the Sleep Calculator do?

What inputs do I need?

Typical inputs include Desired wake-up hour in 24-hour format., Length of one sleep cycle (typically 90 minutes)., Average minutes needed to fall asleep..

How are the results calculated?

We follow the formulas and assumptions outlined in the "How this calculator works" section. You will see outputs like Bedtime for 6 full sleep cycles (~9 hours)., Bedtime for 5 full sleep cycles (~7.5 hours)., Bedtime for 4 full sleep cycles (~6 hours)..