Half Marathon Training for Beginners: How the Weeks Are Built
Patricia Bedoya
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7
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Cover image generated with AI — © Chubby Studio S.L.
KEY TAKEAWAY
A beginner half marathon plan usually runs 12 to 16 weeks at three runs a week: two short easy runs and a long run that grows by about a kilometre a week to 16 to 18 km, then a taper. Start from around 15 km a week, keep almost everything easy, and never make one run more than about 10% longer than your longest of the past month.
A beginner half marathon plan usually lasts 12 to 16 weeks, with three or four runs a week: two or three short easy runs and one long run that grows to around 16 to 18 km, followed by a short taper. The real job of those weeks is not reaching 21.1 km in training. It is growing from the running you do now without any single jump your legs are not ready for.
That second part is the one most plans leave unsaid. Below is how the weeks are put together, using one of the few half marathon schedules researchers have actually followed with GPS data, and what your watch can tell you along the way. If you are still deciding whether you have enough time, start with how long it takes to train for a half marathon.
What does a beginner half marathon plan look like week by week?
Most beginner plans share one shape: three runs a week, most of them easy, with the weekly long run doing the heavy lifting. Volume rises slowly for about ten weeks, peaks two or three weeks before the race, then drops so you reach the start line rested rather than tired.
ProjectRun21, a study run from Aarhus University in Denmark, gives a useful concrete example because its schedules were written for research and published in full. All three versions lasted 14 weeks with three runs a week, 42 sessions in total. In the distance-based version, two of the weekly runs stay short, mostly 5 to 6 km, while the third grows by about a kilometre a week: 8 km in week one, 12 km in week five, 18 km in week eleven. Then it steps back to 15 km, then 12 km, and then the race. That schedule averaged about 26 km a week.
Nothing in that plan is clever, and that is the point. The structure is repetitive on purpose. The two short runs stay the same week after week, so only one thing changes at a time: the long run.
How many days a week should you run for a first half marathon?
Three is enough for most beginners. Every schedule in ProjectRun21 used three runs a week, and most published beginner plans use three or four. A fourth day helps once three feel routine, but it should be a short, easy run, not another demanding one.
The days between runs are part of the plan. Spreading the three runs out, for example Tuesday, Thursday and the weekend, gives each one a day to settle before the next. If you want to move on the other days, a walk or an easy bike ride keeps the habit going without adding impact.
What should you be able to run before you start?
Roughly 15 km a week, spread over a few runs, is a sensible floor before a 12 to 14 week half marathon block. That number comes from ProjectRun21's results: of the 784 runners who followed its schedules, 136 reported an injury during the 14 weeks, and those who had been running less than 15 km a week tended to get hurt more often.
It is worth being precise about how strong that is. The gap was about 11 percentage points, but the confidence interval crossed zero, so the study could not rule out chance, and the authors word it carefully: low-volume runners "may sustain more" injuries. Runners slower than 6:00 per km showed a similar tendency, which the researchers treat as another marker of how much load the body is used to, not as a reason to run faster. Read it as a direction, not a cutoff.
The wider context is less ambiguous. As the ProjectRun21 researchers note, more than 30% of half marathon runners get injured over a year. If you are well under 15 km a week today, the shortest route to the start line is usually a few weeks of building that base before the plan itself begins.
See how your body takes the training
FitWoody reads your Apple Watch data, scores every run by its cardiac load and tracks your training load week by week, next to your HRV and resting heart rate against your own baseline. Comes with a 7-day free trial.
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How long should the long run get before race day?
Most beginner plans top out between 16 and 19 km, not the full 21.1 km. The ProjectRun21 distance-based schedule peaked at 18 km, three weeks before the race. The taper and race day usually carry you through the last few kilometres, which is why plans stop short rather than rehearsing the whole distance.
How the long run grows matters more than where it ends. In a cohort of 5,205 runners followed for 18 months, Frandsen and colleagues found that a single run more than 10% longer than your longest run of the past 30 days raised the injury rate, by 64% for spikes of 10 to 30%, while week-to-week changes in total volume showed no link. After a 12 km long run, that puts the next step at about 13 km. We go through that study, and the weaker case for the 10% weekly rule, in why most running injuries are a load problem.
Do beginners need speed work for a half marathon?
No. For a first half marathon the goal is to finish in control, and easy running builds almost everything that takes. The distance-based ProjectRun21 schedule had no fast running at all until race day. Its pace-based sibling put about a fifth of its kilometres at quicker paces, but over fewer kilometres in total.
Easy means conversational: you could talk in full sentences. Most new runners find that pace feels almost too slow, which is normal and is the same logic behind 80/20 running, where about four in five sessions stay easy. Walking breaks on the long run are fine too. A half marathon finished with a run-walk rhythm is still a half marathon.
If you want one quicker element once the long run passes 12 km or so, a few short strides at the end of an easy run once a week is plenty. Structured intervals can wait for your second half marathon.
What do cutback weeks and the taper do?
They let the training land. A cutback week trims the long run and the weekly total for a few days every third or fourth week, so your body can absorb what came before. The taper does the same before the race: in ProjectRun21 the long run fell from 18 km to 15 km, then 12 km, and the final week held two short runs of 8 and 4 km before the half marathon itself.
Do you need to eat during a half marathon?
For most beginners, a little, yes. Many first half marathons take two hours or more, and in his review of carbohydrate intake during exercise, Jeukendrup gives up to about 60 g of carbohydrate per hour as the recommendation for efforts of two to three hours, against only small amounts for efforts of around one hour. The American College of Sports Medicine guidelines he cites give a wider 30 to 60 g per hour.
In practice that can be a gel or a few sports chews every 30 to 45 minutes, with water. Whatever you plan to eat on race day, try it on your long runs first, so your stomach has met it before the start line.
How can you tell from your watch that the plan is working?
Three signals are worth watching over the weeks. Your easy runs at the same pace should show a gradually lower heart rate, or the same heart rate at a slightly quicker pace. Your resting heart rate and HRV should hold steady or improve against your own baseline, rather than drifting the wrong way for days. And your weekly training load should climb in a smooth line, with the dips of cutback weeks, rather than in sudden steps.
None of these can tell you whether a tendon is coping. Pain that sits in one spot, gets worse as you run or changes how you move belongs with a physiotherapist or doctor, not with a chart.
This is where FitWoody fits today. It reads your Apple Watch data, scores each run by the cardiac load it cost you, tracks your training load over the weeks and compares your HRV and resting heart rate with your own baseline each morning. You can set custom heart rate zones so that easy means your easy, and replay a long run with Flyover to see where the hills pushed your heart rate up. It informs rather than diagnoses, and an Apple Watch is required.
Where to start this week
Add up what you ran over the last two weeks and divide by two. If it is around 15 km a week or more, count back 12 to 14 weeks from race day, find your current longest run and grow it by about a kilometre a week. If it is well below, spend the first month building that base. A first half marathon is built in the quiet middle weeks, not on race day. Showing up, in any form, counts.
Frequently asked questions
How many weeks do I need to train for my first half marathon?
Twelve to sixteen weeks is typical if you already run around 15 km a week comfortably. If you run less than that, add a few weeks of building that base first, so the plan itself starts from a level your legs are used to.
Do I need to run 21 km before race day?
No. Most beginner plans peak with a long run of 16 to 19 km two or three weeks before the race, then taper. Growing the long run gradually matters more than covering the full distance in training.
Can I walk during a half marathon?
Yes. Walking breaks are common and allowed in most road races. A planned run-walk rhythm, practised on your long runs, often gets beginners to the finish feeling better than trying to run every step.