Understanding your result
How it works
Remaining = dose × ½ ^ (hours ÷ 5)
Caffeine has a half-life of about five hours in most adults, so half is gone after 5 hours and three-quarters after 10. Because it lingers, experts suggest avoiding caffeine within about 6–8 hours of bedtime. Sensitivity varies — some people clear it faster or slower.
⚕️ A general estimate. Individual metabolism, pregnancy, medication and genetics change how fast you clear caffeine. Adults are generally advised to stay under ~400 mg/day.
Questions
How long does caffeine stay in your system?
With a ~5-hour half-life, a dose is mostly cleared after about 10 hours, though small amounts remain longer.
How much caffeine is too much?
Healthy adults are generally advised to keep below 400 mg a day; pregnant people below 200 mg.
Sources
Evidence-based · last reviewed July 2026