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☕ Caffeine Bedtime Calculator

Find the latest safe time to drink coffee or caffeine before bed

Sleep Settings
5% (very sensitive)25% (tolerant)
Caffeine Sensitivity
Caffeine Source
Latest Safe Caffeine Time
2:00 PM
Have your last coffee by this time
2:00 PM
Latest Safe Time
19
mg at Bedtime
8.5
Hours Needed
5.5 hrs
Half-Life Used
Average
Sensitivity
4:30 PM
Optimal Window (8h)
Caffeine Level Over Time (from intake)

How to Read This Chart

The orange line shows your caffeine level starting from when you drink. The purple dashed line marks your bedtime. The green zone below the red threshold line is "safe" for sleep. Aim to drink caffeine when the orange line will cross below the threshold before your bedtime.

How Caffeine Affects Sleep

Caffeine works by blocking adenosine receptors in the brain. Adenosine is a chemical that builds up throughout the day and makes you feel sleepy. By blocking these receptors, caffeine prevents you from feeling tired.

Even if you can fall asleep after caffeine, it measurably reduces slow-wave (deep) sleep and REM sleep — the most restorative sleep stages.

Caffeine Half-Life & Genetics

The average caffeine half-life is 5-6 hours. However, the CYP1A2 gene determines how quickly your liver metabolizes caffeine:

  • Fast metabolizers (1A allele): Half-life 3-4 hours. Coffee rarely disrupts sleep.
  • Average metabolizers: Half-life 5-6 hours. Standard 6-8 hour cutoff applies.
  • Slow metabolizers (1F allele): Half-life 7-10 hours. Even morning coffee can disrupt sleep.

Factors that slow caffeine metabolism: pregnancy, oral contraceptives, liver disease, some medications. Factors that speed it up: smoking, regular exercise.

Common Caffeine Sources

SourceServingCaffeine (mg)
Espresso shot1 oz63
Drip coffee8 oz95
Cold brew16 oz200
Energy drink16 oz150-160
Green tea8 oz45
Black tea8 oz47-50
Dark chocolate1 oz12-25
Soda (cola)12 oz35-40

Adenosine & Sleep Pressure

Adenosine is a byproduct of brain activity that accumulates while you're awake, creating "sleep pressure." Caffeine doesn't eliminate this adenosine — it only blocks the receptors temporarily. When caffeine clears, all that blocked adenosine floods back at once, which is why caffeine crashes feel so abrupt.

Planner Settings
Monday
Total mg190
Sleep Impact--
Tuesday
Total mg190
Sleep Impact--
Wednesday
Total mg190
Sleep Impact--
Thursday
Total mg190
Sleep Impact--
Friday
Total mg190
Sleep Impact--
Saturday
Total mg95
Sleep Impact--
Sunday
Total mg95
Sleep Impact--
Weekly Summary
--
Daily Avg (mg)
--
Weekly Total (mg)
--
vs 400mg/day Limit
--
Sleep Quality Score
Weekly Caffeine Intake

How to Use This Calculator

1

Enter Caffeine Intake

Input the amount of caffeine consumed and the time of consumption.

2

Set Bedtime

Enter your planned bedtime to see how caffeine affects your sleep.

3

View Caffeine Timeline

See caffeine levels at bedtime and recommended cutoff time.

Formula & Methodology

Caffeine Half-Life

Remaining = Dose x (0.5)^(Hours / Half-Life)

Caffeine's half-life is 5-6 hours on average. After 5 hours, half the caffeine remains in your system.

Cutoff Time

Cutoff = Bedtime - (Half-Life x 2)

Two half-lives before bed keeps caffeine below 25% of initial dose, minimizing sleep disruption.

About this calculation · Accuracy & Methodology

Key Terms

Half-Life
The time for caffeine concentration to decrease by 50%. Average is 5-6 hours but ranges from 3-9 hours based on genetics and liver function.
Adenosine
A brain chemical that promotes sleepiness. Caffeine blocks adenosine receptors, making you feel alert.
Sleep Latency
The time it takes to fall asleep. Caffeine can increase sleep latency by 15-45 minutes depending on timing and sensitivity.

Real-World Examples

Example 1

Afternoon Coffee

200mg caffeine (large coffee) at 2:00 PM, Bedtime: 10:00 PM

Result: ~75mg remaining at bedtime (37.5%). May still affect sleep quality. Recommend cutoff by 12:00 PM.

Example 2

Morning Only

150mg caffeine at 7:00 AM, Bedtime: 10:30 PM

Result: ~12mg remaining (8%). Negligible impact on sleep.

Caffeine and Sleep: Finding Your Balance

How Caffeine Disrupts Sleep

Even when you fall asleep normally, caffeine reduces deep sleep (slow-wave sleep) by up to 20%. You may sleep the same hours but wake less rested. Studies show caffeine consumed 6 hours before bed still reduces total sleep time by over an hour.

Individual Variation Is Huge

Genetics determine your caffeine metabolism speed. 'Fast metabolizers' clear caffeine in 3-4 hours, while 'slow metabolizers' may take 8-9 hours. If you feel wired from afternoon coffee, you are likely a slow metabolizer.

The 10-Hour Rule

A conservative guideline: stop caffeine intake 10 hours before bedtime. For a 10 PM bedtime, that means no caffeine after noon. This ensures less than 25% remains at bedtime for most people.