People often want a single number. In practice, caffeine lasts “longer than you think” if your half-life is longer or your dose is higher.
Caffeine doesn’t disappear suddenly. It fades gradually. That’s why late-afternoon caffeine can still be present at bedtime.
More caffeine means it takes longer to fall below a threshold. Two coffees can be very different from one.
If you have multiple drinks, use the levels curve tool to see how the total stacks and carries forward.
No. This guide is educational. If you have health concerns or take medications, talk to a clinician.
Use the tools first, then come back here if you want the “why” behind the numbers.