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Questions, awkwardly answered.

Health · Caffeine clock

Caffeine Half-Life Clock

Estimate how much caffeine is still active in your system, when it will clear to sleep-friendly levels, and what your sensitivity profile means for timing.

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Caffeine clock

Enter your coffees today, when you last had one, your weight, and your sensitivity level to get an active caffeine estimate and clearance time.

What this means

This clock estimates remaining caffeine from your total intake and timing using a half-life model adjusted for your sensitivity and body weight.

Formula used

Remaining mg = total mg × 0.5^(hours / half-life). Half-life adjusted for sensitivity and body weight.

Worked example

3 coffees (285mg), 4 hours ago, 75kg, normal sensitivity — remaining caffeine is around 100mg, clears to sleep-friendly levels in about 3 more hours.

Common questions

What counts as sleep-friendly caffeine levels?
This tool uses 30mg as a rough clearance threshold. Below that level, most people find caffeine has a negligible effect on sleep onset, though individual sensitivity varies.

Why does body weight affect the result?
Caffeine is distributed through body water, so a higher body weight generally means a slightly lower peak concentration per kg and a modestly longer clearance time.

Plain-English summary

Enter your intake and timing to find out how much caffeine is still running and when it will clear.

This section translates the result into a short, direct takeaway rather than leaving the page at a bare number.

Disclaimer: This is a general estimate using average caffeine content (95mg per coffee) and a population-level half-life model. Individual metabolism varies significantly. This is not medical advice.

Read the guide

How long does caffeine stay in your system

A plain guide to caffeine half-life, the variables that speed or slow clearance, and what it means for sleep timing.

Read the guide

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