Half-Marathon Fueling: How Many Gels and When?

Two gels can mean very different things. Two packets containing 25 g of carbohydrate give you 50 g total: 25 g/hr over a two-hour half marathon, or 20 g/hr over two and a half hours.

For a half marathon lasting roughly 90 minutes to two and a half hours, 30-60 g/hr is a useful range to practice. A runner racing closer to an hour may benefit from smaller amounts, and gels are only one way to get those carbs. The Australian Institute of Sport's duration-based guidance is the starting point here, rather than a blanket rule that everyone needs two packets.

So yes, fueling is worth planning for most recreational half-marathon race times. But how many gels belong in your pocket depends on their carb content, your finish time, any sports drink, and what you've actually practiced.

Start with your time on course

The AIS guidance separates sustained high-intensity efforts of 45-75 minutes, where small amounts of carbohydrate can help, from endurance exercise lasting 1-2.5 hours, where it recommends 30-60 g/hr. Those bands overlap; they aren't a switch that flips at a particular minute.

For the half marathon, I'd use them like this:

• Around an hour to 75 minutes: a smaller amount may suit the job. You don't need to copy a two-hour runner's packet schedule.
• Roughly 90 minutes to two and a half hours: build a practiced plan within 30-60 g/hr, counting drinks as well as food.
• Longer than two and a half hours: keep planning by duration, effort and tolerance. Crossing that time boundary doesn't mean you suddenly need 90 g/hr.

For a 75-90-minute finish, the AIS 1-2.5-hour range also applies; you can use it to plan a modest, practiced intake instead of treating 90 minutes as a cutoff.

Longer finishes need context. Jeukendrup's review of carbohydrate recommendations describes higher intakes for prolonged exercise, but also says recommendations should come down when absolute exercise intensity is low. Its higher targets largely concern trained athletes. A runner taking three hours to finish shouldn't read an upper-end endurance recommendation as a compulsory feeding rate.

The same review doesn't scale during-exercise carbohydrate recommendations directly to body weight. Women and smaller runners shouldn't automatically halve a plan, and larger runners shouldn't automatically double it. The useful adjustment comes from the event demands and your own tolerance.

These are research-based ranges for planning and practice, not a prediction of exactly when any individual will run out of fuel.

How many gels does that work out to?

Read carbohydrate per packet, rather than packet weight or calories. A hypothetical 25 g gel below means it contains 25 g of carbohydrate.

The calculation is simple:

Planned race carbs = practiced grams per hour × finish time in hours

Then subtract any planned drink carbs before dividing the remainder by the carbs in each gel. If the answer isn't a whole packet, adjust the combination to something you've rehearsed. Still in your pocket? That gel hasn't added any carbs to your intake.

Here are examples using 25 g gels and no sports drink, landing toward the lower end of the range. These are hypothetical plans to rehearse, not prescriptions or minimums. All times are minutes after crossing the start line.

Finish time	Gels during the race	Example gel times	Total carbs	Average
1:30	2	20, 60 minutes	50 g	About 33 g/hr
2:00	3	20, 60, 100 minutes	75 g	37.5 g/hr
2:30	3	25, 75, 125 minutes	75 g	30 g/hr

Those totals exclude breakfast and any pre-start gel. Keep those separate when you pack, otherwise the packet you ate in the corral can quietly become one of the packets you were counting on during the race.

A higher practiced target changes the count. Four 25 g gels over two hours, perhaps at 15, 45, 75 and 105 minutes, give 100 g ÷ 2 = 50 g/hr. Two of those gels give 25 g/hr, which falls below the 30-60 g/hr range, though it still provides carbohydrate. Neither calculation tells you what your stomach will tolerate.

Planning a marathon after this race? The EnduranceOS planner supports marathons, but doesn't currently have a half-marathon preset. Use the arithmetic here for this race rather than selecting the wrong distance.

Use the clock, then check the aid stations

"Take a gel at mile five" leaves a lot unsaid. That could be 35 minutes into one runner's day and an hour into another's. Elapsed time makes the schedule easier to match to the plan you practiced.

But the aid-station map still gets a vote.

The AIS sports-gel guidance says most gels should be taken with water or another dilute fluid, while some products are specifically formulated to be used without water. Follow your packet's directions and rehearse that combination. If your gel needs water, line up its timing with access to water instead of swallowing it and hoping the next station appears soon.

You can move the example times around to fit the course. The point is a manageable pattern with the intended total, not hitting minute 45 like it's a second starting gun. A watch reminder can handle the counting while you're busy checking whether that hill was mentioned in the race description.

Gels aren't compulsory, either. Our gels, chews and drink-mix guide covers the practical differences if another format is easier to use.

Sports drink counts toward the total

Suppose you've practiced a two-hour plan with two 25 g gels and a measured amount of sports drink containing 30 g of carbs:

50 g from gels + 30 g from drink = 80 g total ÷ 2 hours = 40 g/hr

That's a different plan from two gels with water, even though the gel count is identical.

Check the actual drink label and how much you'll drink. For a hypothetical drink containing 6 g per 100 mL, 300 mL provides 18 g. A few uncertain mouthfuls from course cups aren't automatically a full bottle's worth of carbs.

And don't make extra drinking the price of reaching your carb target. The AIS guidance treats fluid and fuel needs separately: gels or other foods can supply carbs when drinking enough sports drink to cover them wouldn't fit your fluid needs. If course-drink amounts are uncertain, keep that uncertainty in the plan rather than pretending every cup is identical.

Rehearse the whole morning

Pick a familiar breakfast and test its timing before race day. The pre-race breakfast guide covers that part in more detail; here, the job is making sure breakfast, a possible pre-start gel and your during-race plan work together.

Could you open the packet, take it at your intended effort and get the water you needed? Did the amount feel comfortable? Those answers are more useful than finding a gel brand with a faster runner on the box.

The AIS recommends practicing gels in training and adjusting for individual gut tolerance. Our gut-training guide gives that practice some structure. If a planned amount repeatedly causes problems, revise it before race day rather than forcing the table above to work.

Write down the product, carb grams, packet count and approximate times once you've found a setup that suits you. Small enough for a phone note. That leaves fewer decisions to make when you're pinning on a bib and trying to remember where you left your shoes.

Write down what you'll actually take

For this half, the useful answer is a practiced carb amount translated into packets and drinks you can actually carry and consume. No universal two-gel rule, and no promise that a packet at mile five will rescue every rough final mile.

A half-marathon schedule shouldn't automatically become your marathon plan. If that's your next step, the marathon gel guide walks through counting fuel over the longer distance.

When you're ready to plan that future marathon, build it in the EnduranceOS planner. Keep the half-marathon timing note for this start line.