Marathon Fuelling by Finish Time: Sub-3, Sub-3:30, Sub-4 and Sub-5 Plans

Most marathon fuelling advice is written as if every runner is the same. They aren't. A runner chasing sub-3 is burning through glycogen at roughly 1,000 kcal an hour and has under three hours to take on board whatever they need. A runner aiming for five hours is moving far more gently, spending more time on their feet, and has a very different problem: staying fuelled, hydrated and mentally sharp for a long, long day. The right marathon fuelling plan depends heavily on how long you will be out there.

The common thread is simple. Your body stores roughly 400-500g of carbohydrate as muscle and liver glycogen, enough for around 90 minutes to two hours at marathon effort. After that, you are either topping up from the outside or slowing down. Below is how we would structure fuelling for four common finish times, with real numbers you can adapt in training rather than trying for the first time on race day.

Why Finish Time Changes Your Carbohydrate Target

Two things shift as you get faster: the proportion of energy coming from carbohydrate, and how much your gut can realistically absorb. At sub-3 pace you are running at a high percentage of your threshold, so carbohydrate supplies the vast majority of your fuel. At a five-hour pace you rely more on fat, which lowers the hourly carbohydrate demand, though the total time on course raises the total amount you need to get through.

As a working guide, the current sports nutrition consensus sits at 30-60g of carbohydrate per hour for efforts between one and two and a half hours, and up to 90g per hour for longer, harder efforts where the gut has been trained to cope. Above about 60g an hour, you need a mix of glucose and fructose (a 2:1 or close to 1:0.8 ratio), because they use different transporters in the gut and together allow higher absorption than glucose alone.

Fluid and sodium matter too. Aim for roughly 400-800ml of fluid an hour depending on temperature and sweat rate, and 300-600mg of sodium an hour if you are a heavy or salty sweater. Slower runners are out for longer, so overdrinking is a bigger risk than most people realise. Drink to thirst rather than to a schedule you have written on your wrist.

Sub-3 and Sub-3:30: Fuelling at Pace

Sub-3 (about 6:50 per mile): you are asking a lot of your gut at high intensity. Target 70-90g of carbohydrate per hour, starting early. Take your first fuel at 20-25 minutes, then every 20 minutes or so. Little and often works better than big hits, because blood flow to the gut drops at this effort. Practise at race pace in your long runs: if you have never taken 80g an hour during a hard session, race day is the wrong time to start.

Sub-3:30 (about 8:00 per mile): aim for 60-80g per hour. This is the zone where a lot of runners feel good about their gels and still hit trouble around mile 18 because they either started too late or fell behind. A simple rule is to set a watch alert every 15 minutes and take a small amount of carbohydrate each time, rather than relying on aid stations.

• Start fuelling by minute 20-25, not when you feel hungry.
• Take 15-25g every 15-20 minutes, using a glucose and fructose mix.
• Sip water with each feed rather than gulping at aid stations.
• Consider caffeine (around 3mg per kg of bodyweight) at the halfway point or mile 18 if you tolerate it.

Your Marathon Fuelling Plan for Sub-4 and Sub-5

This is where most runners sit, and where the advice gets surprisingly vague. A sound marathon fuelling plan for sub 4 (about 9:00 per mile) targets 60g per hour, which works out at around 240g across the race. Break that into 15g every 15 minutes, or 30g every half hour if you prefer fewer stops. Because you are running at a lower relative intensity, your gut usually copes better than a faster runner's, so this is achievable for most people with a few weeks of practice.

For sub-5 (about 11:30 per mile), the target eases to 45-60g per hour, but the challenge shifts from absorption to appetite and consistency. Five hours is a long time, and flavour fatigue sets in. Mix your sources: some pastilles or chews, a banana or a few salted potatoes at aid stations, and fluids with carbohydrate in them. Keep the plan boring and repeatable, and set reminders rather than relying on how you feel, because after three hours most runners stop wanting to eat.

Whatever your pace, the last six miles are where an under-fuelled runner slows dramatically. If you have kept up your hourly intake, you should still have enough glycogen and blood glucose to maintain form. If you have not, no amount of gritted teeth will fix it. Aim to have fuelled consistently for at least the first 20 miles.

Training Your Gut Before Race Day

The gut is trainable. Over six to eight weeks, build your carbohydrate intake in long runs: start at 40g an hour, then climb by 10g every week or two until you reach your target. Use the exact products you plan to race with. Expect some rumbling early on; that settles as the gut adapts. If something causes persistent issues, change the product, not the target.

Your pre-race preparation matters too. In the 36-48 hours before, aim for 8-10g of carbohydrate per kg of bodyweight per day, keep fibre lower, and avoid anything unfamiliar. On race morning, eat 1-2g per kg of carbohydrate two to three hours before the start, then top up with a small amount of fuel about 15 minutes before the gun.

What We Use at FTP Endurance Fuel

We built FTP Endurance Fuel around exactly this problem: taking carbohydrate in small, regular amounts without the stickiness and stomach heaviness of gels. Our energy pastilles are easy to carry in a vest pocket or shorts, and you can take one at a time, which makes pacing your intake against a 15-minute watch alert very simple. Check the label for the carbohydrate content per serving and do the sums against your target before race day.

Many runners like the Mixed Fruit flavours for variety across a long race, while the Tart Cherry Pastilles 1kg bring a sharper, less sweet flavour, which can help when sweetness starts to wear thin in the later miles. If you want to test before you commit to a big bag, the Taster Pack is a low-risk way to try them on your long runs.

Pick the finish time that matches your training, build your gut over the coming weeks, and rehearse your plan until it is automatic. Race day should be about running, not improvising. When you are ready to put your plan into practice, browse our bundles and stock up for your long runs and the big day itself.