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Triathlon · Sprint to Ironman

Triathlon Fueling Calculator

Per-leg carb, fluid, and sodium targets for swim, bike, and run — from sprint to Ironman. Built to avoid the classic “over-fueled bike, wrecked run” mistake.

Updated 17 April 2026 · Sara Klein, Contributor

Quick answer

On the bike, front-load calories: 60-90 g carbs/hour, 500-800 mL fluid/hour, 500-900 mg sodium/hour. Taper the last 20 minutes before T2. On the run, drop to 40-60 g carbs/hour, sip at every aid station, and don't try to catch up on missed bike calories.

Your race

Why per-leg matters

The most common triathlon nutrition failure is over-fueling the bike. It feels easy to eat on the bike — you're seated, the stomach is stable, and there are bottle cages everywhere. Athletes take on 90+ g/h for 5 hours, then step off in T2 with a stomach full of sugar and nowhere to send it. The run leg becomes a slow walk to GI disaster.

The fix is asymmetric. Front-load early, taper late, keep the run conservative.

Pre-race (15 min before swim)

A small gel (25 g carbs) topped with 200-300 mL of water is enough. Don't eat solid food in T1 or at the swim start — it will sit in your stomach for the swim.

Bike leg

  • First hour. Aim high: 80-90 g/h if you've trained the gut. Heart rate is lowest, gut tolerance highest.
  • Middle. Cruise at your target carb rate. Mix gels, bars, and drink-mix to avoid flavour fatigue.
  • Last 20 min before T2. Cut solids. Sip water. Maybe a final gel 25 minutes out if it's a long race and you're behind on intake.

Run leg

Conservative. Walk aid stations if you need to — a 10-second walk gets water into the stomach instead of onto your face. One gel every 30-40 minutes and sips of sports drink or cola in the back half. Don't chase bike calories you missed.

Read next

Full race-day plan: Triathlon Race Day Fueling.