From 10K to Half Marathon: Your Training Plan for the Next Step

Already comfortable with 10K and eyeing 21.1 km? A 9-week plan shows how to grow your long run safely – and why it's best run with a group from here on out.

Daniel Gruber · 17 September 2026 · 5 min read

If you've got 10K dialed in, you've already cleared the hardest hurdle: your body knows sustained running, your legs know endurance load, and you know what it feels like to stick with a training plan over several weeks. The half marathon (21.1 km / 13.1 miles) is still its own jump, though – not because it's twice as hard, but because the long run now grows into territory where pacing, fueling, and the mental side raise entirely new questions. If you've already made the jump from 5K to 10K, you know the playbook: easy stays the default, the long run grows slowly, and running it with a group turns a long session into something you actually look forward to.

What you should already have in place

The plans this article draws on – Hal Higdon's half marathon programs (source: Hal Higdon 2026) and the 10K-to-half-marathon plans from Marathon Handbook (source: Marathon Handbook 2026) – assume a baseline: being able to run 10K without being wrecked afterward, and currently running three times a week. That's exactly where you are if you've just finished a 10K plan or regularly join 10K events. Nothing more is required to start.

The plan: 9 weeks from 10K shape to half marathon

Three fixed runs a week, plus an optional fourth easy run or cross-training session (bike, swim, strength) – that's all the step up requires. Notice week 4: a deliberate step-back week where the long run gets shorter instead of longer. That's not a setback – it's the part of the plan that does the most for injury prevention (more on that below).

Why the long run should become a group thing

At 10K distance, 60–75 minutes straight already felt like an achievement. Now the long runs stretch to 90 minutes and beyond – and that's exactly the range where a training plan either survives or quietly falls off the calendar around week 5. Running the long run with a group, at conversational pace (you should be able to hold a conversation the whole way), turns two hours of running into a social outing instead of a solitary chore – and it keeps you honest on pace, because nobody in a group long run wants to turn it into a time trial. An event with others moving at the same pace matters more for the 15–19 km runs from week 5 onward than any pacing app.

Fueling: when you actually need something on the run

At 10K, you can skip gels and drinks entirely. That changes for the half marathon: once you're past roughly 75–90 minutes of effort, fueling starts to matter, because glycogen stores run low. As a rule of thumb, aim for 30–60 g of carbs per hour; most recreational runners cover that with 2–4 gels over a half marathon, spaced 30–45 minutes apart, each with a few sips of water (source: Runners Need 2025, The Feed 2025). Take your first gel around 20–40 minutes in, not once you already feel your energy dip – by then it's usually too late, since absorption takes time. Practice this on your long training runs (week 6 in the plan), never for the first time on race day.

Race-day pacing: even beats euphoric

The biggest mistake in a first half marathon is starting too fast – the start-line adrenaline and the crowd around you pull you along almost automatically. For first-timers, the rule is even pacing over negative splits. Judge your pace by your long-run training pace, and start a few seconds slower than you think you need rather than faster – the second half forgives restraint at the start, but not overconfidence (source: Marathon Handbook 2026).

The science behind the plan: not weekly mileage, one single run

A 2025 study using Garmin-RunSafe running health data (over 5,200 runners, more than half a million logged runs) found something most training plans still ignore: the strongest injury risk factor wasn't the increase in weekly mileage – it was a single run that was significantly longer than the longest run of the past 30 days. A jump of 10–30% raised injury risk by 64%, and jumps over 100% raised it by 128% (source: Nielsen et al. 2025, British Journal of Sports Medicine). That's exactly why this plan grows the long run in small steps with a built-in step-back week, rather than ramping straight up to 21.1 km.

If you're looking for a group running the same long run at conversational pace as you – from 11 km in week 1 all the way to the half marathon itself – you'll find matching run clubs and long-run events in the overview.

1. Week 1 – Settle in 2× 5–6 km easy during the week, plus an 11 km long run at pure conversational pace – ideally with a group, so the pace stays easy on its own.
2. Week 2 – Find your rhythm 2× 6 km easy, plus one run with 4× 1-minute pickups. The long run grows to 12 km.
3. Week 3 – First faster element Alongside the easy runs, an 8 km run at a brisk but still talkable pace. Long run: 13 km.
4. Week 4 – Step-back week Deliberately shorter: just 2× 5 km fully easy and a 12 km long run. This recovery week is part of the plan, not a setback.
5. Week 5 – New distance PR 2× 6 km easy plus a brisker 8 km run. The long run grows to 14 km – still at conversational pace.
6. Week 6 – Test fueling On the 15 km long run, try water and a gel for the first time – not on race day.
7. Week 7 – Race-day dress rehearsal On the 17 km long run, simulate breakfast, shoes, and start time exactly as on race day.
8. Week 8 – Longest long run 18–19 km, the longest run of the whole plan. Taper begins right after – let your legs recover.
9. Week 9 – Taper and race Just 2× 4 km fully easy plus a short 8 km run midweek. At the end of the week: the half marathon, 21.1 km, rested and recovered.

Sources

• halhigdon.com/training-programs/half-marathon-training/novi…
• mymottiv.com/half-marathon-training-plan/10-week-intermedia…
• marathonhandbook.com/trainingplans/half-marathon-training-p…
• bjsm.bmj.com/content/bjsports/early/2025/07/07/bjsports-202…
• marathonhandbook.com/the-10-rule-new-study-suggests-weve-be…
• runnersneed.com/expert-advice/nutrition-and-hydration/energ…
• thefeed.com/insider/fueling-and-hydrating-for-a-half-marath…
• marathonhandbook.com/negative-splits
• mymottiv.com/how-to-train-for-a-half-marathon/how-to-pace-a…