Caffeine dose
calculator

Your performance caffeine dose from bodyweight — 3 to 6 mg per kilogram, about 60 minutes before exercise (ISSN 2021) — with the two things the flat-number tools skip: the fixed safety ceiling the per-kg dose can run past, and how much is still on board at bedtime.

The performance dose is per kilogram — the safety limit isn't

Caffeine reliably improves exercise performance at 3 to 6 mg per kilogram of body mass, taken about 60 minutes before exercise (Guest et al. 2021, the ISSN position stand). For a 154 lb (70 kg) athlete that's 210 to 420 mg. Below the band, roughly 2 mg/kg is about the minimal effective dose; above it, 9 mg/kg adds no more performance and a lot more side effects.

That is the number the flat calculators give. The one they don't: the safety figure is not per kilogram. EFSA (2015) put habitual intake at 400 mg/day and a single dose at 200 mg without safety concern for healthy adults — fixed milligrams. So the two scales collide. At 200 lb (90.7 kg), the 6 mg/kg top of the band is 544 mg, straight past the daily figure, while a lighter athlete never gets near it. The heavier you are, the sooner the performance ceiling and the safety ceiling meet — and the practical top drops toward 3–4.5 mg/kg.

How the math works

The dose is bodyweight times a per-kilogram figure. The safety numbers are read straight from the EFSA opinion. The bedtime residual is caffeine's known elimination applied to a half-life.

Caffeine forms differ in speed but not much in effect at these doses: anhydrous caffeine (capsule or powder) is the most-studied and is absorbed quickly, with blood levels peaking around 45 minutes to two hours after you take it — which is why 60 minutes before is the usual timing.

Worked example

A 154 lb (70 kg) athlete taking caffeine for a hard session, about an hour before it starts:

• Ergogenic band (3–6 mg/kg): 70 × 3 to 70 × 6 = 210–420 mg
• Minimal effective (2 mg/kg): 140 mg  ·  moderate (4.5 mg/kg): 315 mg
• Against the safety figures: the 210 mg start is just over the 200 mg single-dose figure and under the 400 mg daily; the 420 mg top is above both

Now a heavier athlete at 200 lb (90.7 kg). The band is 272–544 mg, and the 6 mg/kg top (544 mg) runs well past the 400 mg daily figure — so the useful ceiling for them is nearer 3–4.5 mg/kg (272–408 mg), not the full 6.

Take that first athlete's 200 mg for an evening workout, 4 hours before bed. At caffeine's ~5-hour half-life, 200 × 0.5^(4/5) = 115 mg is still in the body at lights-out — above the 100 mg that can push back sleep. A pre-workout scoop lists its caffeine in a font sized to impress, not to dose; the number that matters is milligrams per kilogram of you, and when you took it.

When this calculator is wrong

The performance dose is per kilogram but the safety limit is a fixed number, so the top of the 3–6 mg/kg band can run past the daily safe intake — and an evening dose can still be blunting your sleep hours later. The dose scales with bodyweight (Guest et al. 2021), but EFSA (2015) put habitual daily intake at a flat 400 mg. At 90 kg, 6 mg/kg is 540 mg, so the band runs straight through the ceiling and the practical top is nearer 3–4.5 mg/kg. And a 200 mg dose taken 4 hours before bed leaves about 115 mg on board, above the 100 mg that can delay sleep.

• The counter-case is a lighter athlete training in the morning. Neither problem bites: 3 mg/kg is well under 400 mg, and a dose taken 12+ hours before bed has decayed to a fraction. The critique is of a flat number that ignores bodyweight at the top of the band and time-of-day at the bottom — the mg/kg dose itself is well supported.
• Individual response is not average response. The ergogenic effect varies between people, partly by CYP1A2 genotype, and the half-life itself ranges roughly 3–7 hours — longer in pregnancy and on oral contraceptives, shorter in habitual smokers. Treat the bedtime figure as an estimate, not a clock.
• Habitual intake shifts the picture. Regular heavy coffee drinkers may see a smaller acute effect, and abrupt changes bring withdrawal. This page doses the session; it doesn't model tolerance built over months.

What to do with the result

Start at the low end — 3 mg/kg — and only move up if you tolerate it and want to. That first dose is also a test: caffeine's effect and its side effects (jitter, a racing heart, GI upset) are individual, so the sensible first trial is a training day, not race day. If 3 mg/kg does nothing, step toward 4.5; there's rarely a reason to reach 6, and above 9 mg/kg you're trading performance for side effects.

Add up every source against the daily figure — coffee, tea, energy drinks, pre-workout, and gels all count. For evening sessions, use the bedtime readout: if it leaves you above ~100 mg at lights-out, take less or take it earlier. Pair this with the water intake calculator and the electrolyte calculator for the fluid and sodium side of the same session.

Common questions

How much caffeine should I take before a workout?

The evidence-based dose is 3 to 6 mg per kilogram of bodyweight, taken about 60 minutes before exercise (ISSN 2021). For a 70 kg (154 lb) athlete that's 210 to 420 mg. Start at the low end and move up only if you tolerate it — the top of the band already reaches the daily safety figure for many people.

Is 200 mg of caffeine enough before a workout?

For most people under about 100 kg, 200 mg is inside the 3 mg/kg starting range and is effective — it's also the single-dose amount EFSA (2015) flags as raising no safety concern. The minimal effective dose is around 2 mg/kg (140 mg at 70 kg), so 200 mg clears that comfortably.

How much caffeine is too much?

EFSA (2015) put habitual intake at up to 400 mg/day and a single dose at up to 200 mg without safety concern for healthy adults. For performance specifically, 9 mg/kg and above adds no further benefit and raises the incidence of side effects (Guest et al. 2021). More is not better past the 3–6 mg/kg band.

When should I take caffeine before exercise?

About 60 minutes before, the most-studied timing. Anhydrous caffeine is absorbed quickly and blood levels peak roughly 45 minutes to two hours after ingestion, so an hour ahead puts the peak near the start of the effort.

Does caffeine before an evening workout affect sleep?

It can. Caffeine's elimination half-life is about 5 hours, so a 200 mg pre-workout dose taken 4 hours before bed leaves around 115 mg in the body at bedtime — above the 100 mg that can delay sleep in some people (EFSA 2015). For evening sessions, take less or take it earlier, and use the bedtime readout above.

Should I dose caffeine by body weight?

For the performance dose, yes — the ergogenic effect scales with body mass, which is why it's given in mg/kg. But the safety ceiling is a fixed number, not per-kg, so heavier athletes hit the 400 mg/day figure inside the 3–6 mg/kg band and should cap nearer 3–4.5 mg/kg rather than the full 6.