Social Jetlag & Chronotype Calculator
Enter your usual sleep onset and wake times for workdays and free days. The calculator shows your midsleep shift, social jetlag, weekly average sleep, and the sleep-corrected free-day midsleep used as an MCTQ-style chronotype estimate.
Absolute social jetlag1 hr 45 min
- Signed social jetlag
- +1 hr 45 min
- Workday midsleep
- 02:45
- Free-day midsleep
- 04:30
- Sleep-corrected free-day midsleep (MSFsc)
- 04:19
- Workday sleep duration
- 7 hr 30 min
- Free-day sleep duration
- 8 hr
- Free-day sleep difference
- +30 min
- Weighted weekly average sleep
- 7 hr 39 min
Sleep schedule comparison
| Schedule | Duration | Midsleep |
|---|---|---|
| Workday | 7 hr 30 min | 02:45 |
| Free day | 8 hr | 04:30 |
| Free day corrected | 7 hr 39 min | 04:19 |
Clock times use a 24-hour day and wrap across midnight when the sleep interval crosses midnight.
How to use this calculator
- Enter sleep onset, not the time you get into bed, for a typical work or school night.
- Enter the wake time for that same constrained schedule.
- Enter sleep onset and wake time for a free day when waking is not forced by an alarm or obligation.
- Set the number of constrained days in the week, then compare the midsleep and MSFsc results.
How the calculation works
Social jetlag compares the midpoint of your main sleep episode on constrained days with the midpoint on free days. The calculator first converts each clock time to minutes after midnight. If a wake time is earlier than sleep onset, the sleep interval is treated as crossing midnight.
The workday sleep duration is SDw = mod(EWw - SOw, 1440). The free-day duration is SDf = mod(EWf - SOf, 1440). Workday midsleep is MSW = mod(SOw + SDw / 2, 1440), and free-day midsleep is MSF = mod(SOf + SDf / 2, 1440).
With W work or school days and F = 7 - W free days, weekly average sleep is SDweek = (W × SDw + F × SDf) / 7. Signed social jetlag is the shorter circular-clock difference: SJLrel = mod(MSF - MSW + 720, 1440) - 720. Positive values mean free-day midsleep is later. Absolute social jetlag is |SJLrel|.
The sleep-corrected free-day midsleep, usually written as MSFsc, adjusts free-day midsleep earlier when free-day sleep is longer than workday sleep. This follows the Munich Chronotype Questionnaire convention: MSFsc = mod(MSF - (SDf - SDweek) / 2, 1440) when SDf > SDw. When free-day sleep is not longer, MSFsc stays equal to MSF.
What moves the result
The largest driver is the distance between the two midsleep points, not the distance between bedtimes alone. Sleeping from 23:00 to 06:30 has a midsleep of 02:45; sleeping from 00:30 to 08:30 has a midsleep of 04:30. That schedule has 1 hour 45 minutes of absolute social jetlag. The workday count also matters because it changes the weekly average used in the MSFsc correction.
Circular time is important. A free-day midsleep at 00:30 and a workday midsleep at 23:30 are one hour apart, not 23 hours apart. If the two midsleep points are exactly 12 hours apart, there is no unique shorter direction, so the signed result is labeled ambiguous.
What this calculator leaves out
This is a schedule comparison, not a direct measurement of circadian phase. It assumes one main sleep episode and a repeating seven-day pattern. It does not model naps, rotating shifts, split sleep, travel, daylight-saving changes, time-zone changes, sleep latency, sleep quality, or biological markers such as dim-light melatonin onset.
Worked example
Suppose workday sleep onset is 23:00 and workday waking is 06:30. Workday sleep duration is 7 hours 30 minutes, so workday midsleep is 02:45. On free days, sleep onset is 00:30 and waking is 08:30. Free-day sleep duration is 8 hours, so free-day midsleep is 04:30.
The free-day midsleep is 1 hour 45 minutes later than the workday midsleep, so absolute social jetlag is 1 hour 45 minutes and signed social jetlag is +1 hour 45 minutes. With five workdays and two free days, weighted weekly average sleep is about 7 hours 39 minutes. Because free-day sleep is longer than workday sleep, MSFsc adjusts from 04:30 to about 04:19.
Common questions
What is social jetlag?
Social jetlag is the mismatch between sleep timing on constrained days and free days. In this calculator it is measured as the circular-clock difference between workday midsleep and free-day midsleep.
How do I find midsleep when the interval crosses midnight?
Use the elapsed sleep duration, then add half of that duration to sleep onset and wrap the result back onto a 24-hour clock. For example, 23:00 to 06:30 is 7 hours 30 minutes of sleep, so midsleep is 02:45.
What is the difference between signed and absolute social jetlag?
Absolute social jetlag is the size of the midsleep shift, ignoring direction. Signed social jetlag keeps the direction: positive means free-day midsleep is later than workday midsleep, and negative means it is earlier.
What does MSFsc mean?
MSFsc means sleep-corrected midsleep on free days. It adjusts free-day midsleep earlier when longer free-day sleep appears to include recovery sleep above the weekly average.
Can shift workers use this calculator?
Shift workers can use it as a simple comparison between two recurring schedules, but the result may be hard to interpret. Rotating shifts, night work, split sleep, and irregular weeks break the assumptions behind a single MCTQ-style workday and free-day pattern.
Do naps count toward the calculation?
No. The calculation uses one main sleep episode for workdays and one for free days. Regular naps can affect total sleep and sleep timing, but they are outside this calculator.