Before building our caffeine intake calculator, we looked at how the commonly-cited 400mg/day guidance actually gets used — and how well it fits different people.
How much caffeine is safe per day, really?
The FDA's 400mg/day figure for healthy adults is a population average, roughly calibrated for a 160lb (~72kg) adult. That means it's too high for someone who weighs considerably less, and unnecessarily conservative for someone who weighs considerably more. A flat number applied to everyone was never meant to be precise for any one person.
Daily caffeine limit calculator — by body weight, not just a flat number
A more personalized rough guide several sources cite: about 6mg of caffeine per kg of body weight, capped at the FDA's 400mg ceiling either way. Our calculator shows both numbers side by side — the flat limit everyone quotes, and your own weight-based estimate if you enter your weight.
What about pregnancy?
The American College of Obstetricians and Gynecologists recommends capping caffeine at 200mg/day during pregnancy, regardless of body weight — a separate, lower number this calculator notes explicitly rather than folding into the main estimate.
