How long does caffeine stay in your system?

Caffeine typically takes 10-12 hours to be almost fully cleared from your system. After one half-life (5-6 hours), 50% remains. After two half-lives (10-12 hours), 25% remains. Most people feel caffeine's effects for 4-6 hours, though traces remain longer.

How does this caffeine calculator work?

Enter the amount of caffeine you consumed (in mg or by selecting a drink type) and the time you consumed it. The calculator uses the standard 5-6 hour half-life to show you how much caffeine remains in your system at any given time, visualized on a decay chart.

What affects caffeine metabolism speed?

Several factors affect how fast you metabolize caffeine: genetics (CYP1A2 enzyme variants), age, liver function, pregnancy (half-life doubles to 9-11 hours), smoking (speeds up metabolism), and medications like oral contraceptives (can slow metabolism by 50%).

When should I stop drinking coffee to sleep well?

A good rule is to stop caffeine intake at least 8-10 hours before bedtime. If you sleep at 10 PM, your last coffee should be around noon to 2 PM. Even small amounts of caffeine can reduce sleep quality, even if you don't feel fully awake.

How much caffeine is in a cup of coffee?

An 8 oz cup of brewed coffee contains about 80-100mg of caffeine. Espresso has about 63mg per shot. Cold brew can have 150-200mg per cup. Energy drinks range from 80mg to 300mg. Tea has 25-50mg per cup.

Caffeine Half-Life Calculator

Calculate how long caffeine stays in your system. Free caffeine half-life calculator with metabolism visualization and sleep impact analysis.

Calculators

Instant results

Your Caffeine Intake

at:

Caffeine Half-Life: 5 hoursAverage: 5 hours (3-7 range)

2h (fast metabolizer)10h (slow metabolizer)

Total Intake

95 mg

Peak Level

95 mg

at 8:00 AM

At Bedtime (10 PM)

14 mg

Sleep-Safe Time

1:00 PM

below 50 mg

Caffeine Level Throughout the Day

50mg sleep threshold

12:00 AM

0 mg

1:00 AM

0 mg

2:00 AM

0 mg

3:00 AM

0 mg

4:00 AM

0 mg

5:00 AM

0 mg

6:00 AM

0 mg

7:00 AM

0 mg

8:00 AM

95 mg

9:00 AM

83 mg

10:00 AM

72 mg

11:00 AM

63 mg

12:00 PM

55 mg

1:00 PM

48 mg

2:00 PM

41 mg

3:00 PM

36 mg

4:00 PM

31 mg

5:00 PM

27 mg

6:00 PM

24 mg

7:00 PM

21 mg

8:00 PM

18 mg

9:00 PM

16 mg

10:00 PM

14 mg

11:00 PM

12 mg

Above 50mg (daytime) Above 50mg (nighttime) Below 50mg

Caffeine Guidelines

FDA recommends a maximum of 400mg per day for healthy adults
Caffeine half-life averages 5 hours but varies from 3-7 hours based on genetics, age, and medications
Sleep experts suggest keeping caffeine below 50mg at bedtime
Pregnant women should limit intake to 200mg per day
Caffeine takes 30-60 minutes to reach peak blood levels after consumption
Smoking can halve caffeine half-life; oral contraceptives can double it

About Caffeine Half-Life Calculator

This tool calculates how caffeine levels decrease in your body over a 24-hour period using exponential decay based on the half-life of caffeine. The default half-life is 5 hours, meaning after 5 hours, half the caffeine is still in your system. Adjust the half-life slider to match your metabolism. All calculations happen in your browser.

How to Use Caffeine Half-Life Calculator

Enter your values

Open Caffeine Half-Life Calculator and enter the values you want to calculate or convert.

Select units or options

Choose the input and output units, formats, or calculation parameters.

View results instantly

Results are calculated in real-time as you type — no submit button needed.

Copy or use the result

Copy the calculated result or use it directly in your work.

Frequently Asked Questions

Caffeine half-life is the time it takes for your body to eliminate half the caffeine in your system. For most adults, caffeine's half-life is about 5-6 hours, meaning if you consume 200mg of caffeine, you'll still have about 100mg in your system 5-6 hours later.

Caffeine Half-Life Calculator

Caffeine Level Throughout the Day

Caffeine Guidelines

About Caffeine Half-Life Calculator

How to Use Caffeine Half-Life Calculator

Enter your values

Select units or options

View results instantly

Copy or use the result

Frequently Asked Questions

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