How much caffeine is too much?

For many healthy adults, 400 mg per day is a common general reference. Sensitivity varies, and pregnancy, medications, heart conditions and anxiety can require a lower limit.

How long does caffeine stay in your system?

This calculator uses a 5-hour half-life model, meaning about half of a dose remains after 5 hours. Real half-life can be shorter or much longer.

Can caffeine affect sleep 6 hours later?

Yes. Sleep studies have found measurable effects from caffeine taken 6 hours before bedtime, especially in sensitive people.

Does coffee sober you up?

No. Caffeine can make someone feel more alert, but it does not lower BAC or make alcohol leave the body faster.

Should I use label caffeine values or presets?

Use the label when available. Presets are typical estimates and can vary by brand, serving size and brewing method.

Caffeine Calculator

Estimate daily caffeine intake from coffee, tea, energy drinks, chocolate or supplements, then model caffeine left before sleep using a half-life estimate.

Settings

Weight, kg

Daily reference: 399 mg · Single-dose reference: 200 mg

Before sleep, hr

Hours until target bedtime

Today's caffeine

Caffeine, mg

Hours ago

Servings

Total today

63 mg

Within reference

% of daily reference

16%

of 399 mg

Current estimate

63 mg

using ~5 hr half-life

At bedtime

21 mg

Lower sleep-impact estimate

Time to low 50 mg

1 hr 40 min

Conditional sleep estimate, not a guarantee

FDA and EFSA references for healthy adults commonly use up to 400 mg/day and up to 200 mg as a single dose. Pregnancy and breastfeeding often use a lower 200 mg/day reference. Energy drinks are not recommended for children or teens. Half-life can change with pregnancy, medication and oral contraceptives; smoking can speed caffeine metabolism.

Calculate caffeine intake for the day

Caffeine calculator intent is practical: total the caffeine in drinks, foods and supplements, compare it with adult reference levels, and estimate how much may still be active near bedtime.

D_{d a y} = i \sum m g_{i} \cdot n_{i}

Dday - total caffeine today, mgi - caffeine in one serving, ni - number of servings.

L_{d a y} = min (400, 5.7 W)

Lday - daily reference in milligrams, W - body weight in kilograms.

L_{s in g l e} = min (200, 3 W)

Lsingle - single-dose reference in milligrams.

This page is a caffeine-estimate tool, not medical advice. Pregnancy, heart rhythm problems, anxiety, sleep disorders, liver disease and medications can require a lower limit.

Caffeine half-life and sleep

The calculator uses a simple half-life model. English search results increasingly expect a bedtime estimate, but individual caffeine clearance varies a lot.

R = m g \cdot 0. 5^{t /5}

R - estimated remaining caffeine, mg - dose, t - hours after intake, 5 - default half-life in hours.

t_{t a r g e t} = 5 lo g_{2} (\frac{m g}{t a r g e t})

ttarget - hours until a selected remaining-caffeine threshold.

A 50 mg target is a model threshold for a low remaining amount, not an official sleep-safety cutoff.
Drake et al. found sleep effects when caffeine was taken 0, 3 or 6 hours before bedtime.
Pregnancy, some medications and oral contraceptives can slow caffeine metabolism.
Smoking can speed caffeine metabolism; sensitivity can change after quitting.

Reference levels and caveats

Situation	Reference used	How to read it
Healthy adult	Up to 400 mg/day	FDA and EFSA-aligned general reference, not a personal prescription
Single adult dose	Up to 200 mg	EFSA single-dose reference for adults
Pregnancy or breastfeeding	Often 200 mg/day or lower	Discuss an individual limit with a clinician
Children and teens	Avoid energy drinks	AAP warns against energy drinks for children and adolescents
High-concentration caffeine	Extra caution	Pure or highly concentrated caffeine products can cause serious harm from small measuring errors

Chest pain, severe palpitations, seizures, confusion or collapse after caffeine need urgent medical care. Do not use an online calculator to manage suspected overdose.

Frequently Asked Questions

Sources and References

Calculations are based on the listed reference sources. Links open in a new tab.

Updated: June 2, 2026

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