How much caffeine should you take before a race?
3–6 mg per kilogram of body weight, taken about 45–60 minutes before the start, improves endurance performance by roughly 2–4%.
The ergogenic window for caffeine is well established at 3–6 mg per kilogram of body mass. For a 70 kg runner that is 210–420 mg, which is roughly two to four cups of brewed coffee or one to two strong caffeinated gels. The typical performance benefit reported across endurance studies is 2–4%.
Timing follows the pharmacokinetics. Plasma concentration peaks around 45 minutes after ingestion, so taking it roughly 45–60 minutes before the start puts the peak near the beginning of the race. For a marathon, the long half-life means a single pre-race dose stays meaningfully elevated for hours, and additional caffeine mid-race is more about the carbohydrate it arrives with than about topping up.
The dose-response curve flattens. Benefits plateau around 6 mg/kg, while side effects — elevated heart rate, jitteriness, gastrointestinal distress, disrupted sleep afterwards — keep increasing. Above that dose you are buying downside without upside, which makes the common instinct to take more a bad one.
Practise it. Individual response varies substantially, partly through genetic differences in caffeine metabolism, and race morning is the wrong time to find out that your dose gives you an unsettled stomach at 30 km.
Key numbers
| Ergogenic dose | 3–6 mg/kg | body mass |
|---|---|---|
| Performance effect | 2–4% | endurance |
| Timing | 45–60 min before | peak plasma at ~45 min |
Work it out for yourself
Caffeine & stimulants model — Model your own plasma caffeine curve across a race from dose and timing.
Frequently asked questions
Is more caffeine better for endurance?
No. Benefits plateau around 6 mg/kg while side effects keep rising, so higher doses add gastrointestinal risk, jitteriness and elevated heart rate without additional performance. Most runners do better at the lower end of the range than the upper.
Should I take caffeine during a marathon as well as before?
A single pre-race dose stays elevated for hours given the roughly five-hour half-life, so additional mid-race caffeine adds less than runners assume. Caffeinated gels late in a race are reasonable, mostly for the perceived-exertion effect when fatigue is highest.
Sources
- Southward, Rutherfurd-Markwick & Ali (2018). The effect of acute caffeine ingestion on endurance performance. Sports Medicine.
- Pickering & Kiely (2019). What should we do about habitual caffeine use in athletes? Sports Medicine.
Related explainers
Glossary: Caffeine, Dose-Response