Find a safe daily caffeine limit based on your body weight, and see how your current intake compares.
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Caffeine affects everyone differently, but body weight is one of the simplest, most evidence-backed factors in figuring out a reasonable daily limit for you.
This calculator uses roughly 4.5mg of caffeine per kilogram of body weight, capped at 400mg, the general upper limit the FDA associates with a low risk of negative effects for most healthy adults. Lighter individuals get a proportionally lower recommended cap.
Caffeine has a half-life of roughly 5-6 hours in most adults, meaning half of what you consume is still in your system that many hours later. For better sleep, most people do well cutting off caffeine at least 8-10 hours before bedtime.
If caffeine timing is affecting your sleep, check our Sleep Cycle Calculator, and if you are watching your overall intake for heart health reasons, our Health Tracker in Medical can help you log blood pressure alongside it.
It is a general guideline for healthy adults, not a universal safe limit. People who are pregnant, have certain heart conditions, or are sensitive to caffeine should use a lower limit and consult a doctor.
Caffeine is metabolized relative to body mass, similar to how many substances are dosed, so a lighter person generally reaches a given blood concentration with less caffeine than a heavier person.
Given its 5-6 hour half-life, stopping at least 8-10 hours before your bedtime gives your body meaningful time to clear most of it from your system.