Chronotype calculator
Use your usual sleep times to estimate your sleep midpoint, corrected for catch-up sleep on free days.
Circadian sleep timing analyzer
See whether your sleep timing stays steady across a week, even when some nights cross midnight.
Circadian sleep timing analyzer
Example valuesSee whether your sleep timing stays steady across a week, even when some nights cross midnight.
No account needed. Calculations happen in your browser; your entries are not saved or sent to Century.
Example · Average sleep midpoint
03:21
A seven-night diary pattern, not a measured biological circadian phase.
- Average sleep
- 8.1 h
- Typical midpoint shift
- 21 min
How it’s calculated
Each night’s midpoint is halfway between sleep onset and wake time, accounting for midnight. The seven midpoints are averaged on a 24-hour circle so 23:50 and 00:10 average to midnight, not noon. Typical shift is the median absolute circular deviation from that midpoint. Average sleep duration is reported separately. This describes diary timing; it does not measure internal circadian phase or diagnose a disorder.
Reference: Phillips et al.: Sleep regularity and sleep timing
For general wellness information. This tool does not diagnose health conditions or replace medical advice.
Related tools
All tools
Circadian sleep timing analyzer: use your own data
What to enter
See whether your sleep timing stays steady across a week, even when some nights cross midnight.
SRI compares sleep/wake state at corresponding moments across days and needs finer-grained data. This tool summarizes manually entered sleep timing and its variability.
Read the result in context
Each night contributes a midpoint. The tool averages those midpoints around a 24-hour clock and reports how far nights usually shift.
A stable schedule is only one observable feature. This tool does not measure melatonin onset, light exposure, sleep quality or a biological circadian phase.
Where this estimate stops
This analyzer summarizes variation across seven actual nights. The chronotype calculator estimates corrected free-day midsleep from usual workday and free-day patterns.
Follow your sleep timing and recovery over time in Century.
Frequently asked questions
Do I need a sleep tracker?
No. Enter approximate sleep onset and wake times for seven nights from a diary or memory. More accurate records make the pattern more useful.
Is this the Sleep Regularity Index?
No. SRI compares sleep/wake state at corresponding moments across days and needs finer-grained data. This tool summarizes manually entered sleep timing and its variability.
Does a stable midpoint prove a healthy circadian rhythm?
No. A stable schedule is only one observable feature. This tool does not measure melatonin onset, light exposure, sleep quality or a biological circadian phase.
How does this differ from the chronotype calculator?
This analyzer summarizes variation across seven actual nights. The chronotype calculator estimates corrected free-day midsleep from usual workday and free-day patterns.