2–4h
Post-wake peak window
90m
Ultradian sprint cycle
+34%
Focus when timed right
Build Your Circadian Schedule
Takes 30 seconds. Personalised to your biology.
Wake-Up Time
Work Type
What's your chronotype?
Daily caffeine (cups)
cups/day
Your 24-Hour Energy Timeline
Deep Work
Admin
Recharge
Sleep
Cognitive Energy Curve
Alertness index across waking hours · shaded regions = optimal deep work windows
Your Caffeine Timing Plan
Task Routing Guide
Ultradian Sprint Schedule
Your brain operates on 90-min alertness cycles. Work with them, not against them.
The Science Behind Circadian Productivity
Your circadian rhythm is a 24-hour biological clock that governs cortisol secretion, body temperature, and neurotransmitter activity. This creates predictable windows of high and low cognitive performance — which is exactly what this circadian rhythm calculator exposes for you.
Cortisol Awakening Response
Within 30–45 min of waking, your cortisol surges 50–75%. This CAR is your body's built-in alertness trigger. Using caffeine during this window blunts both effects — delay your first coffee to 90 min post-wake.
Ultradian Rhythms (90-min cycles)
Nested within your circadian cycle are ultradian rhythms — 90-minute oscillations of high and low alertness. Elite performers work in 90-min sprints with 15–20 min breaks to stay in deep flow.
The Post-Lunch Dip
Between 1–3 PM, core body temperature dips and adenosine accumulates — even if you skip lunch. This is biologically the worst time for analytical tasks, but ideal for creative brainstorming or a short nap.
Melatonin & Wind-Down
Melatonin secretion begins ~2 hours before your natural sleep time. Avoid bright screens and important decisions in this window. Use it for low-stakes planning, journaling, and preparing tomorrow's priorities.
Circadian Rhythm Calculator — FAQ
A circadian rhythm calculator takes your wake time and chronotype to predict daily peaks of cognitive alertness, energy slumps, and optimal rest windows — based on cortisol rhythms and 90-minute ultradian cycles.
Most people reach peak cognitive performance 1.5–4 hours after waking, when cortisol is highest. A secondary peak occurs 9–11 hours post-wake. Night owls shift these windows 2–3 hours later.
Caffeine is most effective 90 minutes after waking, after your natural cortisol peak fades. Taking it immediately blunts both the cortisol response and the caffeine effect. Avoid caffeine after your 10th waking hour to protect sleep quality — it has a 5–7 hour half-life.
Your chronotype is your genetic tendency for when you feel most alert and sleepy. ~15% are Early Birds, ~15% are Night Owls, and ~70% are "Third Birds" in between. On a free day with no alarm, note your natural wake time — that reveals your chronotype.
The model is based on published circadian neuroscience (cortisol awakening response, ultradian rhythms, adenosine kinetics). Individual variation exists — use your schedule for 1 week and adjust based on your actual experienced energy levels.