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.

Free, no sign-up. Your numbers in, a clear target out.

Calculator

Find Your Caffeine Window

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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

Your caffeine window7:30 AM → 3:00 PM(7.5 hrs)

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.

01

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

Go deeper with the Stress & Cortisol ProtocolThe complete framework for cortisol timing, HPA axis health, and stress management.Read

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