What is a caffeine half-life?

Half-life is the time it takes for the amount of caffeine in your body to drop by about half. People can have very different half-lives, so this tool treats results as estimates.

How do you calculate remaining caffeine?

This calculator uses an exponential decay model: remaining = dose × (0.5)^(time ÷ half-life). It is a planning model, not a guarantee.

What is a good cutoff time for caffeine before bed?

There is no universal rule. It depends on your dose, your half-life, and your sensitivity. This tool estimates a cutoff time based on a low-remaining threshold so you can test what works for you.

Can this calculator predict how I will sleep?

No. It estimates remaining caffeine from a simplified model. Sleep depends on many factors (routine, stress, light, exercise timing, and nutrition habits).

What if I had multiple coffees during the day?

A multi-dose model sums the decay from each dose. This v1 is intentionally single-dose for speed and simplicity.

Caffeine Half-Life Calculator (Remaining at Bedtime)

About This Calculator

Caffeine does not "wear off" instantly. It declines over time, often modeled as a half-life: after each half-life period, about half of the caffeine remains. This free caffeine half-life calculator estimates how much caffeine might still be in your system at bedtime based on the dose you had (mg), when you had it, and your chosen half-life. It also gives a practical cutoff-time estimate for reaching a low remaining-caffeine threshold by bedtime. This is an educational estimate only. Real caffeine clearance varies widely between people and can be influenced by many factors, so use the result as a planning guide, not a guarantee. If you want more stable energy without relying on caffeine, BeyondCal focuses on nutrition quality beyond calories, including micronutrients and electrolytes that support consistent daily performance.

Estimate remaining caffeine at bedtime from a simple dose and time
Choose a half-life to match your personal sensitivity
Get a suggested caffeine cutoff time before sleep
Copy a clean summary of your result
Improve energy fundamentals beyond caffeine in BeyondCal

Safety note

Educational calculator only. It does not provide medical advice, diagnosis, or treatment. If you have symptoms, take medications, are pregnant, or have medical conditions, review results with a licensed clinician or registered dietitian before acting on them.

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How It Works

Caffeine declines by half-life: This model assumes caffeine decreases exponentially. Each half-life, about half remains.
Dose and timing drive the result: A higher dose or a later time increases what may remain at bedtime.
Half-life varies a lot: People can have very different caffeine half-lives. That is why you can adjust it here.
Cutoff time is a planning tool: We estimate when you would need to stop caffeine to reach a low remaining amount by bedtime.

Frequently Asked Questions

Disclaimer: Educational estimate only. Not medical advice. Caffeine half-life varies widely person to person.

Read full disclaimer

This calculator provides an educational estimate of remaining caffeine based on a simplified half-life decay model. It does not provide medical advice, diagnose conditions, or predict sleep outcomes. Individual caffeine clearance varies and can be influenced by many factors. If you have health concerns or questions about caffeine intake, consult a qualified professional.

Get energy without late-day caffeine chaos. This tool estimates what caffeine might still be doing at bedtime. BeyondCal helps you build more stable energy by tracking nutrition quality beyond calories, including micronutrients and electrolytes that support consistent daily performance.

Try it for free!