Sleep Consistency Calculator

1. Pick a typical week. Use a sleep diary, your phone alarm history or a tracker for the last seven nights.
2. Enter each night. Add the time you fell asleep and the time you woke the next morning, Monday night to Sunday night.
3. Set your days off. Choose Saturday and Sunday if you work a standard week, or no fixed days off if every day is different.

Sleep consistency, also called sleep regularity, is how closely your sleep and wake times match from one day to the next. Two people can both average 7.5 hours a night; one sleeps 11 PM to 6:30 AM every night, the other swings between 9 PM and 3 AM. Their sleep length is the same, but their regularity is very different.

Researchers measure it with the Sleep Regularity Index (SRI), introduced in a study that followed 61 university students with sleep diaries for 30 days. Irregular sleepers had a body clock that ran later: their evening melatonin rise came at about 12:08 AM, versus 9:32 PM in regular sleepers, and their SRI was linked to their academic performance.

Consistency is separate from sleep debt: you can be regular but short of sleep, or get enough hours at very irregular times.

The calculator lays your seven nights on a minute-by-minute timeline, marks each minute as asleep or awake, then compares every minute with the same minute 24 hours later.

1. Six day-pairs are compared (Monday with Tuesday, up to Saturday with Sunday): 8,640 minutes.
2. If every minute matches, the SRI is 100. If sleep and wake were random, it would be close to 0.
3. Variation is the standard deviation of your seven sleep times, wake times and night lengths.
4. Social jetlag is the average mid-sleep on Friday and Saturday nights minus the average on the other five nights.

Mid-sleep is the halfway point between falling asleep and waking. To see how your mid-sleep relates to your chronotype, use the circadian rhythm calculator.

Priya sleeps 11:00 PM to 6:30 AM on work nights. On Friday and Saturday she stays up until 12:30 AM and sleeps in until 9:00 AM.

Five identical nights keep her SRI high, but her wake time swings by 2.5 hours at the weekend. That 2-hour social jetlag is like flying two time zones west every Friday and back every Monday, which is why the verdict is capped at fair. Waking by 7:30 AM on free days would cut her social jetlag to about an hour without losing much sleep.

Wake Time

The time you get up, and the morning light that follows it, anchors the body clock. Irregular sleepers in the student study also had weaker daily light patterns.

Work And School Start Times

Early starts on weekdays and free mornings at weekends create social jetlag. Teens are hit hardest because their body clock runs late; see teen sleep deprivation.

Evening Screens And Late Plans

Late light and social plans push bedtime later on some nights but not others.

Shift Work And Travel

Rotating shifts and time-zone changes make regular timing hard by design; plan them separately rather than judging yourself by the SRI.

Both matter, and regularity may matter more than people think. In 60,977 UK Biobank adults who wore activity trackers, the typical SRI was 81, with the middle half of people between 73.8 and 86.3. Compared with the least regular fifth, people in the other four fifths had a 20% to 48% lower risk of death from any cause over about 6 years, after adjusting for age, lifestyle and health factors, and regularity predicted mortality better than sleep duration did.

These are observational findings: they show links, not proof that changing your schedule will change your risk.

Social jetlag is the gap between the middle of your sleep on work days and on free days. It describes the mismatch between your body clock and your social schedule. In the large MCTQ database, about 40% of people had 1 hour or less, 29% had 1 to 2 hours, 12% had 2 to 3 hours and 5% had more than 3 hours.

• People who feel worse on Mondays than on Fridays, a common sign of weekend drift.
• Students and young adults with changing class, work and social schedules.
• Anyone trying to fix their sleep who wants a before-and-after number; our guide to why sleep schedules keep failing covers the usual reasons.

1. Fix your wake time first. The AASM advises getting up at the same time every day, even at weekends and on holiday.
2. Set a bedtime that allows enough sleep, at least 7 to 8 hours, and only go to bed when sleepy.
3. Get daylight soon after waking to anchor your body clock.
4. Keep weekend lie-ins short, ideally within an hour of your work-day wake time.
5. Avoid caffeine in the afternoon and evening and large meals late at night.

Entering Time In Bed Instead Of Sleep

Use the time you fell asleep, not the time you lay down, or the score will look more regular than your sleep really is.

Using An Unusual Week

A holiday, illness or travel week will not reflect your normal pattern.

Chasing 100

Small differences of 15 to 30 minutes are normal. Aim to cut large swings, not to sleep by the minute.

Ignoring Sleep Length

A regular schedule that only allows 6 hours still leaves you short of sleep.

The arithmetic is exact for the times you enter, but a diary week is a small sample.

Above 81 is better than the typical adult in a large UK study, and above 86 puts you in the most regular quarter. Scores from a diary run a little higher than tracker scores.

Record when you fell asleep and woke up for seven nights, then compare each minute with the same minute a day later. The calculator does this for you.

A short lie-in is fine, but sleeping in by two hours or more shifts your body clock and makes Monday mornings harder. Keep free-day wake times within about an hour.

Wake time. A fixed wake time with morning light anchors the body clock, and bedtime tends to settle around it within a week or two.

Differences of 15 to 30 minutes from night to night are common. Swings of an hour or more on a regular basis are worth reducing.

Large studies link irregular sleep with poorer health, including higher mortality risk, even when sleep length is similar. These studies show links, not proof of cause.

Regular timing does not mean you are getting enough sleep or good quality sleep. Check your average sleep, and see a doctor if you snore loudly or feel sleepy in the day.

Not exactly. Trackers count short awakenings and naps, which lower the SRI, so a diary-based score from this calculator is usually higher.

Many people see a steadier pattern within one to two weeks of keeping a fixed wake time every day, including weekends.

• Phillips et al. Irregular sleep/wake patterns are associated with poorer academic performance and delayed circadian and sleep/wake timing (Scientific Reports, 2017) (SRI definition; 61 students; later melatonin onset)
• Windred et al. Sleep regularity is a stronger predictor of mortality risk than sleep duration (Sleep, 2024) (UK Biobank SRI median 81.0, IQR 73.8-86.3; mortality)
• Roenneberg et al. Chronotype and social jetlag: a (self-) critical review (Biology, 2019) (social jetlag definition and distribution)
• AASM Sleep Education: Healthy sleep habits (same wake time every day; 7 to 8 hours)
• MedlinePlus: Healthy sleep (go to bed and wake up at the same time)