Circadian Rhythm Calculator
Enter your wake time. Get a personalized day — when to get sunlight, stop caffeine, exercise, eat your last meal, dim lights, stop screens, take melatonin, and get in bed — with the science behind each rule.
Your inputs
Your day
Your schedule
Your scheduled wake time. Try to keep this consistent — within 30 minutes — every day, including weekends.
Sleep window begins. Aim for the same bedtime within 30 minutes nightly, including weekends — consistency outperforms duration.
The science behind the schedule
Your circadian rhythm is the master clock that governs sleep, body temperature, hormone release, and dozens of other physiological processes on a roughly 24-hour cycle. The clock takes its cues from three primary inputs: light, food timing, and physical activity.
The most powerful input is light. Bright light hitting the retina within the first hour of waking sets the entire 24-hour cycle. Light in the wrong places — blue light at night, dimness in the morning — drifts the clock and degrades sleep regardless of how many hours you spend in bed.
The second is caffeine timing. Caffeine’s effect on sleep persists much longer than most people think — research shows caffeine consumed even 8.8 hours before bedtime measurably reduces sleep, and consumption 3 hours before bed can phase-delay melatonin by 40 minutes.
Related reading
- Advanced Sleep Phase: Why You Go to Bed at 8 and Wake at 4 AM
- Waking Up Before Your Alarm Every Day? Here's What Your Body Is Telling You
- I Sleep 8 Hours But Still Feel Tired: The Hidden Culprits
- Why You Wake Up at 4am Every Night (And How to Break the Cycle)
- Why Am I Never Tired at Night? (The Real Reasons You're Wired When You Should Be Sleepy)
- Physically Exhausted But Can't Sleep: Why Your Body and Mind Are Out of Sync
FAQ
Does this account for my chronotype (early bird vs night owl)?
The schedule personalizes around your wake time, which captures most chronotype differences. Genuine night owls (DSPS) and early birds (ASPS) tend to feel best when their schedule shifts as a whole — same relative timing rules, just anchored to a different absolute wake.
Why is my caffeine cutoff so early?
Caffeine has a 5-6 hour half-life and a 10-12 hour quarter-life. Even when you fall asleep fine, residual caffeine compresses deep sleep and reduces REM. Studies show 100 mg of caffeine consumed 8+ hours before bed still measurably reduces total sleep time.
What if I'm a shift worker?
Toggle 'Shift worker mode'. The same circadian principles apply — they just need to be anchored to your sleep window rather than the sun. Critical additions for shift workers include strict blackout curtains, blue-light blocking glasses on the commute home, and a strategic light-exposure plan.
Should I take melatonin?
Melatonin works best as a circadian-shift tool (jet lag, delayed sleep phase) at very low doses (0.3-1 mg). It's not a sedative and isn't typically the right tool for ordinary insomnia. If you're considering long-term use, talk to a clinician about your underlying sleep issue first.
What if I can't follow the schedule perfectly?
You don't need to. Hit the high-leverage rules — consistent wake time, morning sunlight, caffeine cutoff, and screens-off — and you'll capture most of the benefit. The schedule is a target, not a contract.