Your GPX track
The file exported by the organiser, Strava, Garmin Connect or Suunto. It carries the terrain: distance and elevation are read back point by point, not typed in by hand.
Tool · Trail & ultra
Trail nutrition calculator, from your GPX
A carb calculator gives you a total. This one gives you a schedule: from your track and your target time, it places every gel, every sip and every bar at the hour and the kilometre where they actually fall.
What the calculator asks for
Your target time
The finish you are aiming for. It is not spread pro rata across kilometres but across the cost of each segment: climbs take their share of time, descents give theirs back.
Your carbohydrate target
A slider from 0 to 120 g/h. You decide; the tool prescribes nothing, it executes the target you set.
What you are carrying
Gels, bars, bottles, refills, with the real quantities in your pack. The calculation sticks to them instead of assuming infinite supply.
What it works out
The time of every intake
One row per intake, as hh:mm from the start, with the product and the quantity.
The matching kilometre
The time translated into a point on the course via the race clock. That is what makes the plan usable on the ground.
Both curves tracked
Cumulative carbohydrate and fluid against their theoretical targets, with the gap at every moment.
Feasibility warnings
Stock exhausted before the finish, a product whose maximum flow rate is below your target: the calculator says so instead of returning a plan you cannot hold.
What it does not work out
Your digestive tolerance. The carbohydrate slider is yours. The tool checks that the plan is achievable with your products, not that your stomach can take it. That is settled in training.
Your late-race drift. The model describes the cost of running by gradient, not accumulated fatigue. Your target time has to account for that already.
Cycling. On a bike, speed depends on power and aerodynamics: different physics, different model. See the cycling page.
Medical advice. Nutrition values are indicative and do not replace guidance from a professional.
Questions about the calculator
›Is the calculator free?
The demo above runs on a sample course, with no account and no card. To compute on your own GPX, the first race is free when you create an account, watch export included. Beyond that a plan costs €2.90, or €19.90 a year unlimited.
›Which files does it accept?
GPX files containing a track with elevation, up to 8 MB. That is the standard export format for trail race organisers, Strava, Garmin Connect and Suunto. A track without elevation is rejected: with no terrain, the calculation would offer nothing over simple arithmetic.
›How does it account for elevation?
Every pair of GPX points gets an effort coefficient derived from the energy-cost polynomials of Minetti et al. (2002), corrected for trail running: the saving from running downhill is only partly converted into speed, braking costs you beyond −10 %, and the model switches to power hiking on steep gradients. Those coefficients are aggregated over 500 m segments, then the target time is spread in proportion to the total cost.
›Does it work out my split times too?
Yes, and that is a tool in its own right: the trail time calculator gives your estimated finish and split times kilometre by kilometre, free and with no account. It is the same race clock that then places your intakes.
›How is this different from a plain carb calculator?
A carb calculator multiplies a duration by a rate and gives you a total: 5 h at 80 g/h is 400 g. Useful, but it tells you neither when to take what, nor whether your pack allows it. Here the total is spread across the real course, product by product, and checked against what you are carrying.
Calculate on my GPX
Need your finishing time first? The split time calculator is free and needs no account. For the long stuff, see ultra running nutrition.