Caffeine Cutoff Time Calculator

About this calculator

Caffeine leaves the bloodstream on a predictable decay curve, with a half-life commonly cited around 5 hours in healthy adults — meaning roughly half of what you drank is still active in your system 5 hours later, a quarter remains after 10 hours, and so on. This calculator works backward from your bedtime using that decay curve to find the latest time you can have a caffeinated drink and still fall to a low-enough residual level by the time you want to sleep.

The half-life varies from person to person — smokers metabolize caffeine roughly twice as fast, pregnancy slows it considerably, and certain medications and liver function shift it too — but the 5-hour figure is the standard reference point used in sleep hygiene guidance. People use a cutoff time like this to plan their last cup of coffee, energy drink, or tea of the day when they have a fixed bedtime, rather than relying on the vague 'no caffeine after 2pm' rule that ignores dose size and individual sensitivity.

Enter your planned bedtime and how much caffeine you plan to drink, and the calculator returns the latest safe time to have it.