Free Circadian Rhythm & Sleep Tools
Free calculators and quizzes, grounded in sleep and circadian research, to help you understand your own timing before you download anything.
Caffeine Half-Life Calculator
Find your last safe coffee for tonight's bedtime, counting what you've already drunk today and your caffeine sensitivity (4, 5.5 or 7 h half-life).
Daily Schedule Generator
Pick your chronotype and wake time for a day timed to your body clock: light, peak focus, the dip, exercise and your last coffee. Copy it or share the link.
Nap Calculator
Find the best time to nap from your wake time and bedtime: your likely afternoon dip, when to lie down, when to set the alarm, and whether a caffeine nap fits.
Daylight Saving Time Planner
A night-by-night plan to shift your sleep before the clocks change, with light and caffeine timing, for the US, UK, Europe, Australia and New Zealand.
Huberman Sleep Cocktail Builder
Magnesium, L-theanine, apigenin and inositol: the doses Andrew Huberman has described, with timing and safety notes.
Jet Lag Planner
When to seek light, avoid light, sleep and have your last coffee after a flight, shifting your body clock about an hour a day.
Chronotype Compatibility Quiz
Compare two chronotypes: typical bedtime and wake gaps, shared awake hours, and practical ways to share a bedroom.
Chronotype Quiz
Are you a Lion, Bear, Wolf, or Dolphin? Eight quick questions to estimate your natural sleep and energy timing.
Social Jetlag Calculator
Measure how far your weekend sleep shifts from your weekdays, using the mid-sleep method researchers use, and see why Mondays feel rough.
Sleep Debt Calculator
Add up your sleep debt over the last five nights and get practical tips to recover without shifting your rhythm.
Morning Sunlight Calculator
Today's sunrise in your city, when to step outside after waking, and for how long. ARC's light timer is 20 minutes; stay out longer under heavy cloud.
Chronotype Visualizer
Slide through the day to see an illustrative cortisol and melatonin curve for your chronotype, hour by hour.
Sleep Cycle Calculator
Find the best times to go to bed or wake up based on roughly 90-minute sleep cycles, so your alarm is less likely to land mid-cycle.
Why We Built Free Circadian Tools
Most health apps track your past. They tell you how poorly you slept last night or how many steps you took yesterday. But by the time you see that data, it is too late to change it. Circadian biology is about predicting and shaping your future. It is about knowing what to do right now to shape tomorrow.
We built these free calculators and quizzes because understanding your biological rhythm should not require a wearable or a subscription. Knowing your chronotype (Lion, Bear, Wolf, or Dolphin) and how long caffeine stays in your system is a good place to start.
Use these tools to establish a baseline understanding of your body's internal clock. When you want the caffeine and light math done for you, one sentence a day explaining why you feel the way you do, and a day plan built around your chronotype, download ARC for iPhone.