When should you stop caffeine?
Set your bedtime and see a gentle cutoff, plus an estimate of what may still remain in your system.
How the estimate works
We model caffeine with exponential decay: remaining dose = starting dose × 0.5(hours ÷ half-life). Your cutoff is the time that brings the estimate near 25 mg by bedtime.
Choose a longer half-life if you tend to be more sensitive or clear caffeine slowly.
Why the result is personal
Two people drinking the same coffee can have different caffeine levels and different sleep effects hours later. Treat the output as a conservative planning prompt, not a blood-level measurement.
The listed drink amounts are rough examples. Actual caffeine content varies by product, serving size, and preparation.
Common questions
How long does caffeine stay in your system?
Caffeine is often modeled with a half-life around five hours, but the real value can vary widely. This calculator lets you use four to seven hours rather than assuming everyone clears it identically.
What does half-life mean?
A five-hour half-life means roughly half of a caffeine dose remains after five hours, one quarter after ten hours, and so on. It does not mean the effect suddenly stops.
Is 25 mg at bedtime safe for sleep?
The 25 mg level is a planning threshold used by this tool, not a universal safe limit. Some people are sensitive to less, while others feel less effect despite caffeine still being present.
What can change caffeine clearance?
Genetics, pregnancy, smoking, medications, liver function, and other factors can alter caffeine metabolism. Ask a clinician about circumstances specific to you.