๐ฏ Marathon Fuel Calculator
How many gels, and when?
Just enter your weight and goal time.
Basic Info
Fueling Strategy
Energy Balance
Race Timeline
Must-Do Before Race Day
Must-Do Before Race Day
1. Practice first โ Test this fueling plan during long runs (20km+). Your gut needs time to adapt to gels (at least 3-4 sessions).
2. Individual variation is huge โ Same weight doesn't mean same needs. Gut sensitivity, sweat rate, and body composition differ. This calculator is a starting point, not a perfect answer.
3. Carb-load the night before โ Consume 8-12g carbs per kg body weight the evening before + race morning to top up glycogen stores.
4. Gel + water are partners โ Always take gels with 3-4 sips of water (100-150ml). Combining gels with sports drinks risks carb overload.
Why do we hit the wall at 30km?
At marathon pace, your body primarily burns glycogen (stored carbs). You only have about 90-120 minutes' worth, running out around 25-30km. When forced to switch to slow fat burning, your legs feel like concrete and pace drops 1-2 min/km. This is 'The Wall' or 'Bonking.' The goal of fueling is to push that wall from 30km to 38km+.
Which strategy should I choose?
๐ข Conservative (30-45g/hr): First marathon, sensitive stomach, half marathon, 'safe finish' goal. ๐ก Standard (60g/hr): Experienced marathoner, trained with gels on long runs, targeting a PR. The most proven strategy. ๐ด Aggressive (90g/hr): Sub-3 to sub-3:30 runners, months of gut training, using dual-carb gels (Maurten, SiS). โ ๏ธ Without practice, risk of nausea/GI distress!
How does this calculator work?
Step 1: Weight ร Distance = Total energy burn (kcal). Step 2: Estimate glycogen stores ~400g (1,600 kcal). Step 3: Burn - Stores = Fueling gap. Step 4: Carb strategy (g/hr) + gel product (g/serving) = gel count & timing. Step 5: Temperature-based hydration guide (350-700ml/hr).
Frequently Asked Questions
Q1. Do I need gels for a half marathon?
If you'll be running for 2+ hours, 1-2 gels are recommended. Under 90 minutes, it's not essential but helps maintain pace in the final stretch.
Q2. Can I use bananas or candy instead?
Absolutely! What matters is carbs, not gels specifically. 1 banana โ 25-30g carbs, a handful of gummy bears โ 20-25g. Gels are preferred for fast digestion and portability.
Q3. Should I reduce gels if drinking sports drinks?
Yes! 500ml of Gatorade/Pocari โ 30g carbs. If you plan to drink sports drinks, reduce gels accordingly. This calculator assumes water + gels.
Q4. What if I feel nauseous during the race?
Slow down โ gut blood flow decreases at high intensity. Take gels in 2-3 small sips instead of gulping, always with water. Training your gut in advance increases tolerance.
Our AI analyzes your fitness, course elevation, weather, and training history to create a personalized fueling strategy in your race report.
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