How many gels do I need for a marathon?

Most marathoners need 5–10 gels, depending on finish time, carb target, and gel size. A 4-hour marathoner targeting 60 g of carbs per hour with standard 22 g gels needs roughly 9 gels: first one 20–25 minutes in, then one every 22 minutes, stopping in the final 20 minutes.

How many carbs per hour should I take while racing?

Current sports-nutrition guidance is 30–60 g per hour for efforts of 1–2.5 hours and 60–90 g per hour for longer races, if your gut is trained for it. Most amateur marathoners do best in the 45–70 g/hr range, rehearsed in at least two long runs before race day.

When should I take my first gel in a marathon?

Take the first gel 20–30 minutes into the race, before you feel you need it. Glycogen depletion is far easier to prevent than to reverse — by the time you feel a bonk coming, it is too late for a gel to fully save the day.

Marathon Fueling Calculator — How Many Gels, When to Take Them

Stop guessing how many gels to carry. Get your carb target, gel count, and a race-clock fueling schedule you can print and rehearse on your next long run.

How this calculator works

Endurance nutrition research converges on a simple picture: for races over ~90 minutes, carbohydrate intake of 30–60 g per hour supports performance, and 60–90 g/hr helps further in longer events if your gut is trained to absorb it. This calculator turns your finish time and carb target into a concrete schedule:

First gel at 25 minutes — fueling works preventively, not reactively.
Even spacing — one gel every (gel carbs ÷ hourly target) hours keeps absorption steady and avoids gut bombs.
Nothing in the final 20 minutes — a gel taken there won't reach your muscles before the finish line.

Always take gels with water, not sports drink — stacking both spikes sugar concentration and is the classic recipe for GI distress. And rehearse the exact plan (same gels, same timing) on at least two long runs before race day.

General guidance, not medical or dietetic advice. If you have diabetes or another condition affecting fueling, work with a professional.

FAQ

Can I count on-course sports drink toward my carbs?

Yes — a typical 6 oz cup of sports drink has 10–14 g of carbs. If you'll grab a cup at most aid stations, you can drop your gel target a notch (e.g., from 60 to 40–45 g/hr from gels). Just find out what brand the race serves and practice with it.

What is "gut training"?

Your intestines adapt to absorb more carbohydrate per hour when you practice fueling during training. Start at the conservative setting on long runs, and increase by ~10 g/hr every couple of weeks until you reach your race target comfortably.

Do I really need gels for a half marathon?

Under ~90 minutes, stored glycogen mostly covers you — one gel around 45–60 minutes is insurance. Over 90 minutes, fueling starts paying off measurably, which is why the calculator will still schedule gels for a 2+ hour half.

Marathon Fueling Calculator

Fueling schedule

How this calculator works

FAQ