Caffeine Window Calculator
The CAR (Cortisol Awakening Response) peaks in the 30–90 minutes after you wake up. Drinking coffee during this window reduces its effectiveness and disrupts your natural cortisol curve. This calculator finds your optimal first coffee time — and your last.
Find Your Caffeine Window
Your caffeine timing
First coffee ✓ Optimal
7:30 AM
90 min after waking — after your cortisol peak clears
Last coffee · Most people
3:00 PM
8 hours before bed — allows most caffeine to clear
Last coffee · Caffeine sensitive
1:00 PM
10 hours before bed — for slow metabolizers
Last-coffee times use an 11:00 PM default bedtime. Set your target bedtime above for a personalized cutoff.
Caffeine half-life averages 5–6 hours but varies significantly by genetics, liver enzymes, and medications. If coffee disrupts your sleep even when you stop early, try the sensitive cutoff.
Why wait 90 minutes?
- 📈The CAR peak: Cortisol spikes 50–100% in the first 30–45 minutes after waking. This natural energy surge is your body's built-in “activation.” You don't need caffeine on top of it.
- ☕Caffeine works by blocking adenosine: If adenosine hasn't accumulated yet (you just woke up), coffee's effect is blunted. Waiting lets adenosine build — then caffeine hits harder and lasts longer.
- 📉The afternoon crash: Hitting caffeine before the CAR clears often causes a sharper afternoon crash because you burned through your receptors while cortisol was already high.
How caffeine disrupts sleep
- ⏱️Half-life: Caffeine has a 5–6 hour half-life in most people. A 2 PM coffee still has ~50% of its caffeine active at 8 PM.
- 🧠Deep sleep reduction: Even when you can fall asleep, caffeine suppresses slow-wave (deep) sleep — the most physically restorative stage. You may sleep but recover less.
- 🧬Genetic variance: CYP1A2 enzyme variants make some people fast metabolizers (clear in 3–4 hours) and others slow (6–8 hours). If you're sensitive, the 10-hour cutoff is the safer bet.
Go deeper with the Stress & Cortisol Protocol
The complete framework for cortisol timing, HPA axis health, and stress management.
