Dose and serving size
A larger dose needs more half-lives to fall below the same bedtime threshold. Labels and brew strength vary, so editable mg values matter.
Caffeine Half-Life Calculator: When to Stop Coffee Before Bed
Your Inputs
Choose a common drink, then edit the caffeine amount if your label differs.
Use 2 for two cups or shots.
Total dose: 95 mg.
Local time today.
The cutoff result aims to be below this amount by bedtime.
Advanced settings
Presets are approximations; use your real-world response when it differs.
~5.0 h average adult
How strongly caffeine affects your sleep.
You can add several cups; we’ll combine them.
Caffeine half-life can be extended by pregnancy, some medications, liver conditions, and oral contraceptive use. Smoking can shorten half-life. Ask a clinician if a health condition or medication makes caffeine risky for you.
Kind rule: information, not judgment.
Results
Latest caffeine time for your bedtime
–
Enter a drink and bedtime
Residual caffeine at bedtime –
Falls below selected threshold –
Estimated bedtime delay –
Estimated sleep affected –
Assumes simple half-life decay and your selected sensitivity. Not medical advice.
Formula details
Run the calculator to see the exact calculation.
Tip: If residual caffeine is above your threshold, try moving the last caffeinated drink earlier, choosing a smaller dose, or switching to decaf.
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How this caffeine half-life calculator works
Caffeine does not switch off when the alert feeling fades. The calculator models caffeine remaining at
bedtime with a half-life: the time it takes for the active amount to drop by half. For each drink, it uses
remaining = dose × 0.5^(hours_until_bed / half_life), then adds the remaining amount from every
drink you entered.
The primary result answers the practical question: when to stop drinking coffee for sleep. Choose a threshold, such as 50 mg or 20 mg, and the tool estimates the latest time a drink of the selected size could be taken while falling below that amount by bedtime. The chart shows the same decay curve from intake through bedtime and into the next morning.
Evidence-backed thresholds
Residual caffeine, subjective alertness, and measurable sleep effects are related but not identical. You may stop feeling wired before caffeine is low, or you may feel calm while sleep timing and sleep depth are still affected. This tool uses 50 mg as a practical sleep-disruption reference point and 20 mg as a stricter near-clear target. Sensitive sleepers may prefer the 20 mg threshold; tolerant sleepers may still want to check both.
These thresholds are decision aids, not medical cutoffs. Sleep response varies with genetics, dose, timing, daily caffeine total, stress, sleep debt, pregnancy, liver function, and medications. If caffeine causes palpitations, anxiety, insomnia, or interacts with a medication, use stricter limits and ask a qualified professional.
Privacy & accessibility: everything runs locally in your browser; inputs aren’t uploaded. Results are announced via ARIA live regions for assistive tech.
Worked examples
What affects your result
Timing and bedtime
The same coffee can be low-risk at 10 AM and high at 5 PM. The calculator measures hours from each drink to your target bedtime.
Half-life and metabolism
Average adult half-life is often around 5 hours, but faster and slower metabolism can shift the cutoff by several hours.
Sensitivity and tolerance
Tolerance may make caffeine feel less obvious, but residual caffeine can still affect sleep for some people. Sensitive sleepers should use stricter thresholds.
Total daily caffeine
Multiple coffees, tea, cola, chocolate, supplements, and pre-workout can add up. Add each drink separately when timing differs.
Health context
Pregnancy, oral contraceptive use, liver conditions, and some medications can extend caffeine half-life. Smoking can shorten it.
Sources and assumptions
Half-life range
Adult caffeine half-life is commonly modeled around 3-7 hours, with individual variation. Source: The Safety of Ingested Caffeine review.
Six-hour sleep timing
A Journal of Clinical Sleep Medicine study found that 400 mg caffeine taken even 6 hours before bedtime had measurable sleep effects. Source: Drake et al., 2013.
Adult daily guidance
The FDA cites 400 mg per day as an amount not generally associated with negative effects for most adults, while noting sensitivity varies. Source: FDA consumer update.
Pregnancy guidance
ACOG describes less than 200 mg per day as moderate caffeine consumption during pregnancy. Source: ACOG Ask ACOG.
Calculator assumptions: one-compartment exponential decay, immediate dose availability, editable drink caffeine values, and a user-selected half-life. It does not estimate blood concentration, diagnose insomnia, or replace medical advice.
FAQ
How long before bed should I stop drinking coffee?
For larger doses, a common starting rule is at least 6 hours before bed. This calculator personalizes that by dose, bedtime, half-life, and your selected 20 mg, 50 mg, or custom threshold.
How much caffeine is still in my body at bedtime?
Use the residual caffeine result. It sums the estimated remaining caffeine from each drink at your target bedtime.
Is 50 mg caffeine enough to affect sleep?
It can be for some sleepers. The tool treats 50 mg as a practical reference point and 20 mg as a stricter near-clear target.
Does decaf contain caffeine?
Yes. Decaf is much lower than regular coffee, but it is not always zero. The preset starts low and stays editable.
Does tolerance protect sleep?
Not fully. Tolerance can reduce how noticeable caffeine feels, but residual caffeine may still affect sleep timing or quality.
What if I drink multiple coffees?
Add each drink with its own time and dose. The calculator combines the residual amount at bedtime and redraws the chart.
What caffeine half-life should I choose?
If unsure, use average adult. Choose fast, slow, pregnancy/oral contraceptive, smoker, or medication-sensitive presets when those better match your situation.