Caffeine Half-Life Calculator
Track coffee, tea, soda, and energy drinks through the day. See your estimated caffeine level now, at bedtime, and when it should fall below a sleep-friendlier threshold.
Log what you drank and when. We use exponential decay with an adjustable half-life.
Most adults land around 5 hours, but metabolism, medications, and pregnancy can shift this.
We'll estimate how much caffeine is still active by then.
Current caffeine level
46 mg
Estimated at bedtime
27 mg
Below 50mg in
Now
Daily total
142 mg
36% of the FDA's 400mg general daily limit.
Sleep recommendation
Stop caffeine by 5:52 PMfor a good night's sleep.
Caffeine timeline
6 AM to 11 PM
This is a planning tool, not medical advice. Sensitivity to caffeine varies a lot between people.
How to Use
- Add each caffeinated drink you had today, including the time you drank it.
- Adjust the caffeine half-life slider if you know you process caffeine faster or slower than average.
- Enter your bedtime to estimate how much caffeine will still be active when you try to sleep.
- Review your current level, bedtime level, daily total, and the recommended caffeine cutoff time.
Frequently Asked Questions
What is the half-life of caffeine?
For most healthy adults, caffeine has a half-life of about 5 hours. That means roughly half the caffeine you consumed is still in your body 5 hours later. Genetics, medications, pregnancy, smoking, and liver function can all change that number.
How much caffeine is too much in one day?
The FDA says up to 400mg of caffeine per day is generally considered safe for most healthy adults. That is about four small cups of brewed coffee, but tolerance varies a lot between people.
Can caffeine still affect sleep if I drink it in the afternoon?
Yes. Even if you can fall asleep, caffeine later in the day can reduce deep sleep, delay melatonin timing, and make sleep feel lighter or less restorative. That is why many people benefit from a caffeine cutoff several hours before bed.
Why use 50mg as a sleep threshold?
There is no universal magic number, but 50mg is a practical benchmark because it is low enough that many people feel less stimulation by then. If you are highly sensitive to caffeine, you may want an even lower target.