How to Fuel a Half Marathon: The Complete Plan by Finishing Time

The Half Marathon Fueling Problem Nobody Talks About

Most fueling advice is written for marathoners. If you're running a half, you've probably heard some version of "you'll be fine with just water." And if you're finishing under 75 minutes, that might be true.

But here's the thing most guides skip: the majority of half marathoners finish between 1:45 and 2:30. At that effort and duration, your glycogen stores are draining fast, your blood sugar matters, and your brain is making decisions about whether to push or slow down based on available fuel. A 2:15 half marathon is a serious endurance effort, and it deserves a serious fueling plan.

The problem is that the plans that do exist are usually marathon plans with the numbers halved. That doesn't work either. The intensity profile of a half marathon is different — you're running at a higher percentage of your VO2 max, burning carbohydrates faster per minute, and you have less margin for error because there's no time to recover from a bad patch.

So let's build a plan that actually fits your race.

Why Finishing Time Changes Your Fueling Plan

Two runners lining up for the same half marathon can have completely different fueling needs. Here's why:

Time on feet matters more than distance. A runner finishing in 1:25 burns through roughly 90 minutes of glycogen. A runner finishing in 2:20 is out there for nearly two and a half hours — well into the window where glycogen depletion becomes a real risk.

Intensity affects fuel source. Faster runners burn a higher proportion of carbohydrates per minute, but they're done sooner. Slower runners burn a smaller proportion per minute but need fuel for longer. The total carbohydrate demand can actually be higher for the slower runner.

Body weight is the variable nobody mentions. A 60kg runner and a 90kg runner finishing in the same time have very different absolute calorie and fluid needs. Generic "take one gel every 45 minutes" advice ignores this completely.

Your Half Marathon Fueling Plan by Finishing Time

Sub-1:30 (Under 90 Minutes)

At this pace, you're finishing before glycogen depletion becomes a serious factor for most trained runners. Your pre-race breakfast does most of the work.

• Gels: 0–1. One gel at 40–45 minutes is optional insurance. Many runners at this pace skip fueling entirely and perform fine.
• Fluid: 3–4 sips at aid stations. Drink to comfort, not to a schedule. At this pace you may not want to slow for aid stations at all.
• Electrolytes: A single electrolyte tablet in the water you drink pre-race is sufficient for most conditions. Add an electrolyte drink at one aid station if it's warm.
• Total carbs during race: 0–25g.

1:30–2:00

This is the threshold where fueling starts to matter. You're out long enough to deplete glycogen but running fast enough that your carbohydrate burn rate is high.

• Gels: 1–2 gels. First gel at 35–40 minutes. Second gel at 70–75 minutes if your finishing time is closer to 2:00.
• Fluid: 150–200ml every 20 minutes. Alternate between water and electrolyte drink at aid stations.
• Electrolytes: One serving of electrolyte drink during the race, plus whatever you took pre-race.
• Total carbs during race: 25–50g.

2:00–2:30

Now you're firmly in endurance territory. Glycogen depletion is a real threat, and under-fueling is the number-one reason runners in this bracket hit a wall in the final 5K.

• Gels: 2–3 gels. First gel at 30–35 minutes. Subsequent gels every 35–40 minutes.
• Fluid: 150–250ml every 15–20 minutes. More in warm conditions.
• Electrolytes: 2 servings of electrolyte drink spread across the race. Critical in heat or if you're a heavy sweater.
• Total carbs during race: 50–80g.

2:30+ (Over Two and a Half Hours)

At this duration, your half marathon has the same fueling demands as many runners' full marathon. This bracket is where under-fueling causes the most damage — and where most generic advice fails hardest.

• Gels: 3–4 gels. First gel at 30 minutes. Subsequent gels every 30–35 minutes.
• Fluid: 200–300ml every 15–20 minutes. Dehydration risk increases significantly at this duration.
• Electrolytes: 2–3 servings of electrolyte drink. Consider a sodium-heavy option if you tend to get white salt marks on your kit.
• Total carbs during race: 75–120g.

The Pre-Race Breakfast That Sets Up Everything

Your fueling plan starts 3–4 hours before the gun goes off. The goal is to top off glycogen stores without sitting heavy in your stomach.

What to eat: 1–2g of carbohydrate per kilogram of body weight. For a 70kg runner, that's 70–140g of carbs. Think porridge with banana and honey, or toast with jam and a glass of juice.

What to avoid: High-fibre foods, high-fat foods, and anything you haven't eaten before a training run. Race morning is not the time for experiments.

Hydration: 400–500ml of water or electrolyte drink with breakfast. Stop drinking large volumes 60 minutes before the start — small sips only after that.

Three Mistakes That Wreck Half Marathon Fueling

Mistake 1: Waiting Until You Feel Bad

By the time you feel hungry, dizzy, or foggy during a race, you're already 15–20 minutes behind on fuel. Glycogen depletion is a slow process, and your body doesn't send you a warning notification at 50%. It sends one at 10% — and by then it's too late to recover.

Start fueling at 30–40 minutes regardless of how you feel. Your first gel should feel almost too early.

Mistake 2: Using a Gel You've Never Tried

Your stomach handles gels differently at race pace than it does sitting on your sofa. The blood flow to your gut drops dramatically when you're running hard, which means gels that feel fine in training at easy pace can cause nausea, cramping, or worse at race effort.

Test your exact gel brand and flavour on at least 3–4 long runs before race day. If a gel makes you feel sick in training, it will make you feel worse in the race.

Mistake 3: Ignoring Conditions

A half marathon on a cool, overcast morning and the same race on a 28°C sunny day are two completely different fueling events. Heat increases your sweat rate, accelerates fluid loss, and makes your gut more sensitive to gels.

For warm races: increase fluid intake by 20–30%, shift toward electrolyte drinks over plain water, and consider taking your gels with extra water to aid absorption.

How to Practise This Plan in Training

Your long runs are your fueling rehearsals. Here's how to use them:

Weeks 12–8 before race day: Start taking one gel on your long runs at around the 40-minute mark. Get your stomach used to processing fuel while running.

Weeks 8–4: Add a second gel and practise your full race-day timing. Run at least two long runs at goal pace while fueling at the intervals you plan to use.

Weeks 4–1: Lock in your plan. Your final two long runs should use the exact products, the exact timing, and ideally similar conditions to race day. Don't change anything in the last week.

If you experience GI distress during any long run, don't abandon the plan — reduce the volume slightly and try again next week. Gut training is a real physiological adaptation: research shows that structured practice reduces gut discomfort by nearly 50% in just two weeks.

Why Generic Plans Fall Short

Every piece of advice in this article comes with a qualifier: "for most runners," "depending on body weight," "in moderate conditions." That's because fueling is personal. Your sweat rate, your body weight, your pace, the temperature, the humidity, your training load in the weeks before the race — all of these shift the numbers.

A 55kg runner finishing in 1:50 on a cool day has a completely different fueling profile from a 85kg runner finishing in 2:20 in the heat. A static plan can get you in the right ballpark, but it can't account for the variables that actually determine whether you finish strong or crawl the last two miles.

This is exactly the problem Sweatr was built to solve. Connect your Apple Watch, Garmin, or Strava data, enter your goal race, and Sweatr calculates a personalised fueling plan based on your actual body, your actual training, and the actual conditions you'll race in. No guesswork, no generic tables — just a clear plan that tells you what to take and when.

Your Pre-Race Checklist

Before you line up, make sure you've sorted these five things:

1. Breakfast tested. You've eaten this exact meal before at least two long runs.
2. Gels packed. You have the right number for your finishing-time bracket, plus one spare.
3. Gel timing memorised. You know the mile or minute marks for each gel. Set watch alerts if your watch supports them.
4. Aid station plan. You know which aid stations you'll drink at and which you'll skip.
5. Conditions check. If it's warmer than your training runs, bump up fluid intake by 20–30% and add an extra electrolyte serving.

Build Your Plan in Two Minutes

You can follow the tables in this article and build a solid half marathon fueling plan manually. But if you want one that adapts to your exact body weight, sweat rate, and race-day conditions — and updates as your training changes — Sweatr does that automatically using your wearable data.

Download Sweatr, connect your watch, and get your personalised half marathon fueling plan before your next long run.