Your race has a shape.
Your pacing should too.
Shaped by heat.
Pacing, weather and fueling in one plan, built for road marathons.
Full plan, completely free ยท One email, one free plan, one free refresh before race day
Marathon pacing that reacts to weather, wind and hills
Same runner, same fitness. Watch the target pace react to conditions.
Km 25 target pace
4:13/km
Calm and below where heat starts to cost you: this is the baseline target pace for this km.
Same course, real grade
Refresh the forecast
One refresh before race day is included, so your splits match the latest forecast.
Race notes in plain words
An AI-written note for the moments that matter most, with every number from the engine.
Fueling on your splits
When to take each gel and how much, so the pace you plan is one you can hold late in the race.
3:02
marathon, plus a sub-1:23 half: the founder's own results
Plans for Berlin, London, NYC, Chicago, Valencia and more ยท km or miles, your call
Even splits are a guess. Yours won't be.
Even splits fail on real courses. Splitshape models the hills, the wind and the late-race fade before the gun goes off.
Pick your course
Choose from 38 major races with verified elevation profiles, or upload any GPX file.
Set your goal
Target time plus a recent result. We check it's realistic, and tell you if it isn't.
Get your strategy
Split-by-split pacing fitted to the course and forecast, coach-style notes on where the race is won, and a gel plan timed to your splits.
Take it with you
Printable pace band, lock-screen card, Garmin course export, and guides for COROS and Apple Watch. Your gels are marked on the band and the course.
Not just numbers. A strategy.
A sample sub-3 plan for the Frankfurt Marathon:
FUELING: The first gel comes at 8 km, around 34 minutes in, once your legs have settled. After that, one gel every 31 minutes keeps your intake steady, so you never chase a deficit.
KM 30โ38: The fade begins here, built into the plan: 4:15/km drifts to 4:18/km. Do not fight it by surging.
KM 40โ42.2: Forecast says 11ยฐC and calm. Empty the tank at 4:08: the finish is indoors, on the red carpet of the Festhalle. Arrive with nothing left.
The gel schedule from the same plan
Why I built this. I ran 3:02 in Warsaw. Two minutes and change from sub-3: the kind of gap you don't close with more training, you close with a smarter race. I'm building Splitshape for my own sub-3 attempt, and every plan it generates is the kind of plan I race with. I'm user #1. Pacing is only half of it. In one marathon, poor fueling on the course and too little carb loading before it cost me my legs late in the race. So Splitshape plans both.
Follow my sub-3 build-up on Strava โPlans for the races you're actually running
Real elevation profiles for 38 marathons and half marathons. See what your course actually asks of you before you commit to a pace.
Marathon pacing & fueling FAQ
How is this different from Garmin PacePro?
PacePro adjusts for elevation only, with generic settings, and it doesn't plan your fueling. Splitshape also models race-day weather, realistic late-race fade, and your recent fitness, adds a gel schedule timed to your splits, and explains the strategy in plain language, so you know why each split is what it is. For Garmin, we export a course file with your splits (and your gels) marked as waypoints; you still build the actual PacePro plan from it inside Garmin Connect (no third-party app can install one directly: that needs Garmin's own partner access).
Does Splitshape include a marathon fueling plan?
Yes. Every plan includes a gel schedule timed to your own splits: when to take each gel, how much, and how many to carry. You set how many carbs per hour your gut is used to (40โ90 g) and enter the gel you train with. There's also a carb loading guide for the days before the race.
Miles or kilometers?
Both. The default follows your race (US and UK races show min/mi, the rest min/km) and you can switch anytime. Pace bands and PDFs come in whichever unit you pick.
My race isn't listed.
Upload the GPX (every race publishes one, or grab it from last year's Strava activities) and you'll get the same full plan.
What if the weather forecast changes?
You can refresh your plan once before race day. Refreshing pulls the latest forecast and re-solves your splits and race notes together, so it's best used when it really counts.
How many gels do I need for a marathon?
It depends on your finish time, the carbs in each gel and how many carbs per hour your gut handles. With the default settings (60 g per hour, 25 g gels), a 3:00 to 5:00 marathon gets 5 to 10 gels on the course, plus an optional one before the start. Your plan works out the exact number from your predicted finish on your course and your own gel.
What is carb loading, and does Splitshape plan it?
Carb loading means eating more carbohydrate than usual in the last days before a race, so you start with your glycogen stores topped up. For a race longer than 90 minutes your plan gives 10โ12 g of carbs per kg of body weight a day for the last 36โ48 hours, plus a pre-race meal of 1โ4 g per kg, 1โ4 hours before the start. Add your body weight and it shows the amounts in grams. It gives amounts and timing, not a meal plan.
Can I use my own gels?
Yes. Enter the carbs per gel and whether it needs water or contains fructose, and the schedule is built around that gel. If your gel also comes in a caffeinated version, you can use it for the second half, capped by a caffeine limit.
Is Splitshape really free?
Yes. Every plan is free, with no subscription and no hidden paywall. Splitshape is an independent side project. If it helped your race and you'd like to support it, you can buy me an energy gel on Ko-fi.
Do you need access to my Strava?
No, a recent race result typed in is enough. Your data is only ever shown to you.
Is a goal time really predictable?
No model owns race day. Splitshape gives you the highest-probability strategy for your goal, and warns you honestly when a goal doesn't match your recent results.
Still have a question? Email hello [at] splitshape.com