Free calculator

Caffeine Half-Life Calculator

Find out how long caffeine stays in your system after your last coffee or energy drink. This calculator uses the average 5-hour half-life of caffeine to show an hourly breakdown of caffeine levels in your body and tells you when it drops below the sleep-safe threshold of 50mg.

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Enter your details

Caffeine Dose

Common doses: Espresso 63mg, Long Black 125mg, Energy Drink 80mg

Time of Consumption

Hour (0-23)

Minute (0-59)

Caffeine Breakdown

Example

Example figures, not your own. Worked for a 200 mg dose taken at 8:00am. Enter your own details and press Calculate.

Sleep-Safe Time

6:00pm

About 10 hours after consumption

Half-Life Reached

100mg

After 5 hours (at 1:00pm)

Hourly Caffeine Level

Time	Hours	Remaining	Level
8:00am	+0h	200mg	Active
9:00am	+1h	174.1mg	Active
10:00am	+2h	151.6mg	Active
11:00am	+3h	132mg	Active
12:00pm	+4h	114.9mg	Active
1:00pm	+5h	100mg	Active
2:00pm	+6h	87.1mg	Declining
3:00pm	+7h	75.8mg	Declining
4:00pm	+8h	66mg	Declining
5:00pm	+9h	57.4mg	Declining
6:00pm	+10h	50mg	Declining
7:00pm	+11h	43.5mg	Sleep-safe
8:00pm	+12h	37.9mg	Sleep-safe
9:00pm	+13h	33mg	Sleep-safe
10:00pm	+14h	28.7mg	Sleep-safe
11:00pm	+15h	25mg	Sleep-safe
12:00am	+16h	21.8mg	Sleep-safe
1:00am	+17h	18.9mg	Sleep-safe
2:00am	+18h	16.5mg	Sleep-safe
3:00am	+19h	14.4mg	Sleep-safe
4:00am	+20h	12.5mg	Sleep-safe
5:00am	+21h	10.9mg	Sleep-safe
6:00am	+22h	9.5mg	Sleep-safe
7:00am	+23h	8.2mg	Sleep-safe
8:00am	+24h	7.2mg	Sleep-safe

How It Works

Caffeine has an average half-life of 5 hours in healthy adults, meaning half the caffeine is eliminated every 5 hours. The formula is: remaining caffeine = initial dose x (0.5)^(hours/5). The calculator plots your caffeine level hour by hour from consumption time and flags when it drops below 50mg, the threshold generally considered safe for sleep.

How to use it

1Enter the amount of caffeine consumed in milligrams
2Enter the time you consumed it (use 24-hour format or AM/PM)
3Click "Calculate" to see the hourly caffeine breakdown
4Check when your caffeine level drops below the 50mg sleep-safe threshold

Quick Reference

Hours After	Caffeine Remaining (%)	From 200mg Dose	Status
0	100%	200mg	Full effect
1	87%	174mg	Active
2	76%	152mg	Active
3	66%	132mg	Active
4	57%	114mg	Active
5	50%	100mg	Half-life reached
7	38%	76mg	Declining
10	25%	50mg	Sleep-safe threshold
12	19%	37mg	Mostly eliminated
15	12%	25mg	Low levels
20	6%	13mg	Trace amounts
24	4%	7mg	Nearly cleared

Based on an average half-life of 5 hours. Individual half-life ranges from 3 to 7 hours depending on genetics, smoking, medications, and liver function.

Caffeine Decay Formula

Remaining (mg) = Dose × (0.5) ^ (t / 5)

Dose: = initial caffeine consumed in milligrams
t: = time elapsed in hours since consumption
5: = average caffeine half-life in hours

Sleep-safe threshold is approximately 50mg. The half-life of 5 hours is an average for healthy adults. Smokers may have a half-life as low as 3 hours; pregnant women may have a half-life of 9-11 hours.

Frequently Asked Questions

What is the half-life of caffeine?

The average half-life of caffeine in healthy adults is approximately 5 hours. This means if you consume 200mg of caffeine, you will have about 100mg remaining after 5 hours, 50mg after 10 hours, and 25mg after 15 hours. Individual variation ranges from 3 to 7 hours.

How late can I drink coffee and still sleep well?

As a general rule, stop consuming caffeine at least 8-10 hours before bedtime. If you go to bed at 10pm, have your last coffee by noon to 2pm. This allows caffeine levels to drop below the 50mg threshold that can disrupt sleep quality.

Does caffeine half-life vary between people?

Yes, significantly. Smokers metabolise caffeine about 50% faster (half-life of 3 hours). Pregnant women metabolise it much slower (half-life of 9-11 hours). Oral contraceptives can double the half-life. Genetics, liver function, and age also play a role.

Can caffeine disrupt sleep even at low levels?

Research suggests that caffeine levels above 50mg can reduce sleep quality, delay sleep onset, and reduce total sleep time. Even if you fall asleep easily, caffeine can reduce the amount of deep (slow-wave) sleep you get, leaving you less rested.

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