CALCULATOR

Caffeine Calculator

Your pre-workout dose at 3 to 6 mg per kg, plus the time to stop drinking caffeine so it does not wreck your sleep.

Caffeine plan

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Pre-workout dose–

Conservative starting dose–

In cups of coffee (~95 mg)–

Take it before training60 minutes

Daily safe ceiling–

Last caffeine of the day–

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Caffeine dosing for performance

The International Society of Sports Nutrition position stand supports 3 to 6 mg of caffeine per kilogram of bodyweight, taken roughly 60 minutes before exercise, for improvements in endurance, muscular endurance, alertness and perceived effort.

This calculator applies that range to your bodyweight and, separately, works out when to stop drinking caffeine so it does not interfere with sleep. Caffeine has a half-life of about five to six hours in most adults, though genetic variation in the CYP1A2 enzyme makes this substantially longer for some people.

The sleep calculation matters more than most people realise. Poor sleep undermines training far more than caffeine assists it, and an afternoon coffee is a common and unrecognised cause of both.

The dosing calculation

ISSN performance rangedose = bodyweight (kg) x 3 to 6 mg
timing = about 60 minutes before exercise

Example, 75 kg:
75 x 3 = 225 mg (conservative)
75 x 6 = 450 mg (upper end)

Sleep cutoffcutoff = bedtime – (half-life multiplier)

Average metaboliser: 8 hours before bed
Sensitive: 10 hours before bed
Fast metaboliser: 6 hours before bed

Dose by bodyweight

Bodyweight	3 mg/kg	4.5 mg/kg	6 mg/kg	Cups of coffee at 6 mg/kg
55 kg	165 mg	248 mg	330 mg	About 3.5
65 kg	195 mg	293 mg	390 mg	About 4
75 kg	225 mg	338 mg	450 mg	About 4.7
85 kg	255 mg	383 mg	510 mg	About 5.4
95 kg	285 mg	428 mg	570 mg	About 6

Note where the upper end collides with general safety guidance. Health authorities commonly cite 400 mg daily as a reasonable ceiling for healthy adults, so anyone above roughly 67 kg reaches that limit at 6 mg per kg from a single pre-workout dose. That is a reason to sit nearer the lower end rather than the top of the range.

Caffeine content of common sources

Source	Serving	Caffeine
Brewed coffee	240 ml	About 95 mg
Espresso	1 shot	About 65 mg
Instant coffee	240 ml	About 60 mg
Black tea	240 ml	About 47 mg
Green tea	240 ml	About 28 mg
Energy drink	250 ml	About 80 mg
Pre-workout	1 scoop	200 to 350 mg
Caffeine tablet	1 tablet	100 or 200 mg
Cola	330 ml	About 34 mg
Dark chocolate	50 g	About 40 mg

Half-life, genetics and why cutoff times differ

Caffeine has a half-life of roughly five to six hours in most adults, meaning half the dose remains that long after drinking it. Take 200 mg at 4pm and roughly 100 mg is still circulating at 10pm.

Individual variation is substantial and largely genetic, driven by the CYP1A2 enzyme that metabolises caffeine. Fast metabolisers clear it quickly and may sleep fine after an evening coffee. Slow metabolisers can be affected many hours later, and research suggests they also derive less performance benefit and more cardiovascular strain from high doses. Pregnancy, oral contraceptives and some medications slow clearance further.

What caffeine does and does not improve

Outcome	Evidence
Endurance performance	Strong and consistent
Muscular endurance	Strong
Perceived exertion	Strong, effort feels easier
Alertness and reaction time	Strong
Maximal strength	Smaller and less consistent
Fat loss	Minor and short-lived metabolic effect

Safety and who should avoid it

400 mg daily is the commonly cited ceiling for healthy adults, and around 200 mg during pregnancy.
Above roughly 9 mg per kg, side effects rise sharply with no added performance benefit.
Cardiac arrhythmias, uncontrolled hypertension and anxiety disorders are reasons to discuss caffeine with a doctor rather than dose by calculator.
Pure caffeine powder is dangerous. A teaspoon can contain a potentially lethal dose, and fatalities have occurred from measuring errors. Use pre-measured tablets or beverages.
Do not stack sources. Pre-workout plus coffee plus an energy drink adds up faster than people expect.

Frequently asked questions

How much caffeine before a workout?

3 to 6 mg per kg of bodyweight, about 60 minutes beforehand. Start at the lower end.

What is the daily safe limit for caffeine?

Health authorities generally consider up to 400 mg daily safe for most healthy adults, and around 200 mg during pregnancy.

How long before bed should I stop caffeine?

At least eight hours for most people, longer if you are sensitive or a slow metaboliser.

Does caffeine tolerance remove the benefit?

Tolerance to alertness develops faster than tolerance to performance effects, so habitual coffee drinkers still benefit.

Sources

Guest NS et al. ISSN position stand: caffeine and exercise performance. JISSN, 2021.
Grgic J et al. Wake up and smell the coffee: caffeine supplementation and exercise performance, an umbrella review. British Journal of Sports Medicine, 2020.
EFSA Panel on Dietetic Products. Scientific Opinion on the safety of caffeine. EFSA Journal, 2015.
US Food and Drug Administration. Spilling the Beans: How Much Caffeine is Too Much. fda.gov
National Institutes of Health, Office of Dietary Supplements. Nutrient fact sheets. ods.od.nih.gov
NHS. Nutrition and health guidance. nhs.uk
US Departments of Agriculture and Health and Human Services. Dietary Guidelines for Americans, 2025-2030. dietaryguidelines.gov

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General information, not medical advice. Consult a qualified professional before changing your diet, especially with a medical condition.