Circadian Rhythm Phase Calculator

Enter your bedtime and wake time to calculate your circadian midpoint, chronotype, social jetlag versus a target phase, and optimal sleep schedule.

Created by Luis GonzalezLast updated: May 9, 2026

How to Use This Calculator

1
Input Bedtime Hour
Enter the hour (0-23, 24-hour format) you typically fall asleep. For example, 23 for 11 PM.
2
Input Bedtime Minute
Enter the minute (0-59) within the bedtime hour you typically fall asleep.
3
Input Wake Hour
Enter the hour (0-23, 24-hour format) you typically wake up. For example, 7 for 7 AM.
4
Input Wake Minute
Enter the minute (0-59) within the wake hour you typically get up.
5
Set Target Midpoint Hour
Input your desired circadian midpoint hour (0-23). The population average is around 3:00-3:30 AM (3-3.5h).
6
Calculate Your Circadian Phase
The calculator will display your actual circadian midpoint, sleep duration, social jetlag, and optimal sleep times to align with your target.

Example Calculation

An individual typically goes to bed at 11:00 PM and wakes up at 7:00 AM. They want to understand their circadian midpoint and how well it aligns with a target midpoint of 3:00 AM.

Bedtime Hour (0–23) (h)

Bedtime Minute (0–59) (min)

Wake Hour (0–23) (h)

Wake Minute (0–59) (min)

Target Midpoint Hour (0–23) (h)

Results

00 AM

Tips

Prioritize Morning Light Exposure

To shift your circadian rhythm earlier (e.g., if you're a night owl trying to become a morning person), expose yourself to bright light (natural sunlight is best) for 20-30 minutes shortly after waking. This helps suppress melatonin and advance your internal clock.

Avoid Late-Night Light

Minimize exposure to blue light from screens (phones, tablets, computers) for at least 1-2 hours before your target bedtime. Blue light can delay melatonin production, making it harder to fall asleep and shifting your circadian midpoint later.

Maintain Consistent Sleep Schedules

Even on weekends, try to keep your bedtime and wake time within an hour of your weekday schedule. Large variations create 'social jetlag,' which can disrupt your circadian rhythm and negatively impact health and mood, as indicated by a high social jetlag score.

Fine-Tuning Your Internal Clock with the Circadian Rhythm Phase Calculator

Understanding and aligning with your body's natural circadian rhythm is fundamental to optimal health, energy, and cognitive function. The Circadian Rhythm Phase Calculator offers a precise way to analyze your current sleep-wake patterns, pinpoint your circadian midpoint, and quantify the impact of social jetlag. By providing your typical sleep and wake times along with a target midpoint, this tool helps you identify how well your daily routine synchronizes with your biological clock and suggests optimal sleep times for better alignment.

Why Your Circadian Rhythm Dictates Your Well-being

Your circadian rhythm, a roughly 24-hour internal clock, dictates far more than just when you feel sleepy. It regulates numerous physiological processes, including hormone release, body temperature, metabolism, and cognitive performance. When your external schedule (e.g., work, social life) consistently clashes with your internal clock, it leads to circadian misalignment, often manifesting as chronic fatigue, impaired focus, and increased risk for conditions like obesity, diabetes, and mood disorders. For instance, studies show that a social jetlag of 2 hours or more is associated with higher rates of depression and metabolic syndrome, underscoring the critical importance of aligning with your natural rhythm.

The Midpoint Formula for Circadian Phase

The core of circadian rhythm analysis in this calculator is the determination of the sleep midpoint. This is the temporal center of your sleep period and a strong indicator of your chronotype.

bed decimal = bed hour + bed minute / 60
wake decimal = wake hour + wake minute / 60
sleep duration = ((wake decimal - bed decimal) + 24) % 24
circadian midpoint = ((bed decimal + sleep duration / 2) % 24 + 24) % 24

The social jetlag is then calculated as the difference between your calculated midpoint and your target midpoint. For example, if you go to bed at 11:00 PM and wake at 7:00 AM, your sleep duration is 8 hours, and your circadian midpoint is 3:00 AM.

💡 Understanding your circadian midpoint is key to optimizing your sleep. If you're looking to establish a consistent sleep schedule, our Ideal Bedtime Calculator can help you work backward from your desired wake-up time to find the best time to go to bed.

Calculating Circadian Phase for a Consistent Sleeper: A Worked Example

Consider an individual who reliably goes to bed at 11:00 PM and wakes up at 7:00 AM. They are aiming for a circadian midpoint of 3:00 AM, which is the population average.

Input Bedtime Hour: 23, Bedtime Minute: 0
Input Wake Hour: 7, Wake Minute: 0
Input Target Midpoint Hour: 3
Calculate Sleep Duration: bedDecimal = 23.0, wakeDecimal = 7.0 duration = ((7.0 - 23.0) + 24) % 24 = (-16 + 24) % 24 = 8.0 hours
Calculate Circadian Midpoint: midpoint = ((23.0 + 8.0 / 2) % 24 + 24) % 24 = ((23.0 + 4.0) % 24 + 24) % 24 = (27.0 % 24 + 24) % 24 = 3.0 The circadian midpoint is 3:00 AM.
Calculate Social Jetlag: social jetlag = |3.0 (calculated) - 3.0 (target)| = 0.0 hours

The primary result, "Circadian Midpoint," is 3:00 AM. This indicates an "Early — typical for morning types" chronotype and "Minimal social jetlag," suggesting excellent alignment between their natural rhythm and their target schedule. The optimal bedtime and wake time would also align with their current schedule.

💡 Beyond the timing of sleep, assessing how efficiently you fall asleep is also crucial for circadian health. Our Sleep Onset Latency Calculator can help you estimate how long it takes you to drift off, a key indicator of sleep quality.

Understanding Circadian Rhythm Benchmarks

The human circadian rhythm, though individual, exhibits certain benchmarks across the population. The average circadian midpoint, as measured by studies using dim light melatonin onset (DLMO), typically falls between 3:00 AM and 4:30 AM. Individuals with midpoints earlier than 3:00 AM are generally considered "morning chronotypes," while those with midpoints later than 4:30 AM are "evening chronotypes." Ideal sleep duration for adults, as recommended by the American Academy of Sleep Medicine (AASM), is 7 to 9 hours per night. A social jetlag of less than 1 hour is generally considered healthy, whereas 2 hours or more is associated with adverse health outcomes. These benchmarks provide a framework for assessing an individual's sleep patterns against population norms.

The Impact of Light Exposure on Circadian Phase Shifting

Light is the most powerful zeitgeber (time-giver) for entraining the human circadian rhythm. The timing and intensity of light exposure directly influence the phase of our internal clock. Exposure to bright light in the morning (e.g., 6:00 AM to 9:00 AM) tends to advance the circadian rhythm, making it easier to wake up earlier and fall asleep earlier. Conversely, exposure to bright light in the evening or late at night (e.g., 9:00 PM to midnight) tends to delay the circadian rhythm, shifting sleep and wake times later. This principle is leveraged in chronotherapy, where controlled light exposure is used to treat sleep disorders like Delayed Sleep Phase Syndrome, gradually shifting an individual's internal clock to a more socially compatible schedule.

Frequently Asked Questions

What is the circadian midpoint and how is it calculated?

The circadian midpoint is the exact halfway point of your sleep period, representing the core timing of your internal biological clock. It is calculated by taking your bedtime, adding half of your total sleep duration, and adjusting for a 24-hour cycle. For example, if you sleep from 11 PM to 7 AM (8 hours), your midpoint is 3 AM. It's a key indicator of your chronotype and alignment with environmental cues.

What is social jetlag and how does it relate to circadian rhythm?

Social jetlag is the mismatch between an individual's natural circadian rhythm (their biological clock) and their social clock (their imposed sleep-wake schedule due to work or school). It occurs when weekend sleep patterns differ significantly from weekday patterns. This misalignment can disrupt the body's natural rhythms, leading to negative health outcomes such as metabolic issues, mood disturbances, and reduced cognitive function, much like actual jetlag.

How can I adjust my circadian rhythm to a target midpoint?

Adjusting your circadian rhythm to a target midpoint involves manipulating light exposure, meal timing, and sleep schedule. To shift earlier, expose yourself to bright light in the morning and avoid light in the evening. To shift later, avoid morning light and expose yourself to light in the evening. Consistency is key, with gradual shifts of 15-30 minutes per day, along with maintaining a regular sleep-wake schedule.