Carbs. Fluid. Sodium. Sorted.
Type your race duration, weight, intensity and expected climate. We build a per-hour fueling plan and tell you how many gels and bottles to pack the night before.
When to take each gel during the race. Sip fluid continuously.
Trained guts absorb about 60 g/h of single-source glucose. Adding fructose (in a 2:1 glucose-to-fructose ratio) lifts that ceiling toward 90 g/h by recruiting a second transporter (GLUT5). Beyond ~90 g/h, the limit is gastric emptying, not absorption — and pushing higher usually means GI distress, not better performance. Below 30 g/h, glycogen depletion drives the late-race "wall" most amateurs experience around 30–35 km of a marathon.
Lay out exactly the gels and bottles your plan calls for, plus one spare gel per hour for safety. Drop bottles every 5 km if you’re self-supported on the bike or running long. Train your gut: practice 80–90 g/h on long sessions for 4–6 weeks before race day. The gut adapts as much as the legs do.
The formulas and ranges above are grounded in the following peer-reviewed literature.
Source for the tiered hourly carbohydrate recommendations: 30 g/h short, 60 g/h up to 3h, 90 g/h beyond with mixed carb sources.
Read paperMultiple-transportable-carbohydrate research — explains why mixing glucose and fructose lets you absorb >60 g/h without GI distress.
Read paperACSM position stand. Source for hourly fluid and sodium ranges by climate.
Read paperVærktøjer der passer godt sammen med dette — åbn i en ny fane og fortsæt med at planlægge.
Compute your 5 training zones from max HR and resting HR. Works for running, cycling and triathlon.
No max-HR test? Pick a formula (Tanaka, Fox/Haskell or Gulati for women), enter your age and get all 5 training zones in BPM.
Weigh yourself before and after a workout and we compute fluid loss per hour, dehydration percent and a per-hour replacement target you can drink.
Convert pace, finish time and distance for any race from 5K to ultra. Includes split times and predicted race times.
About 90 g/h with a glucose + fructose mix (2:1 ratio). This uses two intestinal transporters at once — adding fructose past plain glucose roughly lifts the ceiling from 60 g/h to 90 g/h. Above 90 g/h, gastric emptying becomes the bottleneck and the risk of GI distress climbs sharply.
Sweat rate scales with heat and humidity. In cool conditions you can sweat 400 ml/h; in hot conditions 800 ml/h is common, and elite athletes can hit 1.5+ L/h. We scale fluid by climate and body weight — heavier athletes lose more sweat at the same intensity.
Salty sweaters leave white residue on dark race kit, taste salty after sessions, or cramp despite drinking. They typically need 800–1 200 mg sodium per hour, well above our default 500 mg/h. A sweat test (Levelen, Precision Hydration) gives a precise number; otherwise err high if you cramp on race day.
Yes. The gut is trainable: practice race-day fueling on every long session for 4–6 weeks before race day. Start at 30–40 g/h and add 10 g per session. Most amateurs can comfortably reach 60–70 g/h with practice; well-trained athletes target 90 g/h on marathon and 70.3+ days.
Not really. For races under 90 minutes, glycogen reserves (with a normal pre-race carb meal) are enough. Fluid + a single mid-race gel covers most cases. Fueling targets in this calculator scale down for short, easy efforts and start to matter past the 90-minute mark.
Drafting cuts the work rate at a given speed by 20–30%, lowering carb burn proportionally. If you sit in a peloton for most of an Ironman bike leg, you can run a leaner fueling plan than the headline duration suggests. Solo time-trial riders should plan at the higher end.