What the model does
This calculator starts with an estimated caffeine dose, then applies a constant half-life of 5.7 hours. In a half-life model, the amount is halved after one half-life, halved again after the next, and so on. The result is not a measurement of your blood caffeine level; it is a mathematical illustration.
Why your real result can differ
Caffeine content varies by bean species, dose, beverage size and extraction. Human caffeine metabolism also varies with genetics, age, pregnancy, smoking status, medicines and other factors. That is why this page avoids labeling any specific residual number as universally “safe” or “unsafe.”
How to use the estimator well
Use it to compare timing scenarios rather than to chase a precise biological number. For example, keep the beverage dose fixed and compare 1 PM versus 4 PM. If late caffeine seems to affect your sleep, an earlier cutoff is a practical experiment. Persistent sleep problems deserve individualized advice from a qualified health professional.