Caffeine Half-Life Calculator

Caffeine half-life is the time it takes for your body to eliminate half of the caffeine you consumed. For most healthy adults, the half-life of caffeine is approximately 5 hours. This means if you drink a coffee with 100mg of caffeine, after 5 hours you'll still have about 50mg in your system. After 10 hours, you'll have roughly 25mg remaining.

Caffeine can remain in your system for 10 to 12 hours or more, depending on your metabolism. While you may stop feeling the stimulating effects after 4 to 6 hours, traces of caffeine continue to affect your sleep quality well beyond that. It typically takes 5 to 6 half-lives (about 25 to 30 hours) for caffeine to be almost completely eliminated from your body.

Several factors influence how quickly your body processes caffeine. Genetics play the biggest role, as variations in the CYP1A2 gene determine whether you're a fast or slow metabolizer. Other factors include age (metabolism slows with age), liver function, pregnancy (half-life nearly doubles), smoking (speeds metabolism), oral contraceptives (slows metabolism), and certain medications.

Most sleep experts recommend stopping caffeine intake at least 6 to 8 hours before your intended bedtime. If you plan to sleep at 10 PM, your last coffee should ideally be before 2 PM. However, if you're a slow metabolizer, you may want to cut off even earlier, around noon. Use this calculator to find your personal cutoff time based on your metabolism speed.

The FDA considers 400mg of caffeine per day generally safe for most healthy adults. That's roughly equivalent to four 8-ounce cups of brewed coffee. However, individual sensitivity varies greatly. Pregnant women are advised to limit intake to 200mg per day. If you experience anxiety, insomnia, or heart palpitations, you may want to reduce your intake regardless of these guidelines.

Yes, caffeine metabolism generally slows as you age. Older adults tend to have a longer caffeine half-life, meaning caffeine stays in their system longer. This is partly due to decreased liver function and changes in body composition. This is one reason why many people find they become more sensitive to caffeine's effects on sleep as they get older and may need to reduce intake or consume it earlier in the day.