Endurance supplements
Race day caffeine calculator.
Add up caffeine from coffee, gels and drinks, see it in mg per kg of body mass against the ranges in the IOC and ISSN statements, and find the clock time 60 minutes before the start.
Inputs
Caffeine
Enter your body mass and amounts.
How much caffeine can athletes use in a race?
The IOC consensus statement on supplements describes caffeine at 3 to 6 mg per kg of body mass, taken about 60 minutes before exercise, as a protocol that improves endurance performance, and notes that lower doses (under 3 mg per kg, about 200 mg) before and during exercise with a carbohydrate source have also been used. The ISSN position stand agrees that 3 to 6 mg per kg is consistently ergogenic, says minimal effective doses may be as low as 2 mg per kg, and that doses around 9 mg per kg are associated with a high incidence of side effects. 60 minutes before exercise is the most commonly used timing.
This tool adds the caffeine you enter and divides by body mass. It places the total as below 3, within 3 to 6, above 6 up to 9, or 9 mg per kg and over. It also checks the total against Health Canada's 400 mg per day for adults (300 mg for pregnant or breastfeeding people). Those are research and public health reference points, not a recommended dose. Caffeine affects heart rate, sleep, anxiety and the gut differently in different people, and it stays in the body for hours; the caffeine half-life calculator shows how long.
Frequently asked questions
How much caffeine should I take before a marathon?
The IOC statement describes 3 to 6 mg per kg about 60 minutes before exercise, and lower doses of under 3 mg per kg (around 200 mg) before and during. That is a research range. Whether to use caffeine at all, and how much, is individual and worth testing in training.
When should I take caffeine before a race?
About 60 minutes before the start is the most commonly used timing in the ISSN stand; the tool shows the clock time. Chewing gum may act sooner than capsules.
How much caffeine is too much?
Health Canada gives 400 mg per day for adults 18 and over and 300 mg per day for people who are pregnant or breastfeeding. The IOC and ISSN statements report more side effects at about 9 mg per kg.
Do caffeine gels count?
Yes. Enter how many you will take and the milligrams per gel from the label; the tool adds them to your total.
Sources
Checked
- Maughan et al., IOC consensus statement: dietary supplements and the high-performance athlete, Br J Sports Med 2018
- Guest et al., ISSN position stand: caffeine and exercise performance, J Int Soc Sports Nutr 2021
- Health Canada, Caffeine in Foods (page modified 2025-04-02)
Ranges are quoted from the sources above and are general research or position-statement figures. Gel, powder and drink contents, spare gels and stop intervals are your own inputs; defaults are placeholders. One kilogram of body mass is treated as one litre of fluid.
Scope
Education only, not medical or dietetic advice. Needs differ by person, event, heat and training, and the published ranges are general. Try any fuelling or hydration plan in training, not for the first time on race day. If you have a medical condition (including diabetes, kidney or heart disease or high blood pressure), are pregnant or breastfeeding, or are under 18, ask your doctor or a registered dietitian first. Stop and get medical help for confusion, vomiting, severe headache, fainting or swelling of the hands and feet during or after a long effort.