Add each drink you've had today and set your target sleep time. The calculator shows your total caffeine, how it compares to the 400 mg recommended daily limit, and the latest you can have your next cup without disrupting sleep.
How the sleep cutoff works: caffeine has a half-life of roughly 5.5 hours. The tool solves for the time at which one serving clears to below 50 mg in your system — the threshold where most people stop noticing an effect on sleep onset. Cold brew and double espressos need more runway; a single AeroPress or a tea needs less.
See the coffee to water ratio guide if you want to dial in the strength of your brew first.