Sleep calculator
When to go to bed to wake up refreshed, based on 90-minute sleep cycles.
How it works
A sleep cycle lasts about 90 minutes. Waking at the end of a cycle helps you feel rested; 5 to 6 cycles suit most adults.
Results are for guidance only and do not replace professional advice.
Worked example
With the default values:
- Wake-up time07:00
- Time to fall asleep (min)15
you get:
- Best (6 cycles, 9 h)in bed at 21:45
- 5 cycles (7.5 h)23:15
- 4 cycles (6 h)00:45
- 3 cycles (4.5 h)02:15
Frequently asked questions
How does the “Sleep calculator” tool work?
A sleep cycle lasts about 90 minutes. Waking at the end of a cycle helps you feel rested; 5 to 6 cycles suit most adults.
What do I need to enter?
Just fill in: wake-up time, time to fall asleep. The result updates as you type.
Can you give an example?
Wake-up time: 07:00; Time to fall asleep (min): 15 → Best (6 cycles, 9 h): in bed at 21:45; 5 cycles (7.5 h): 23:15.
Is this calculator free, and is my data private?
Yes. HOD Calc is completely free with no sign-up. The calculation runs in your browser: nothing you type is sent or stored.