How to train for a half marathon: a 12-week training plan
Prepare for a half marathon with a 12-week plan and 4 runs a week. Includes a weekly schedule, long runs, pacing and race-day fueling guidance.
Key takeaways
- For runners who can finish a 10K and run 20–25 km a week.
- Four runs a week; the long run grows from 10 to 18 km.
- Take 30–60 g of carbohydrate per hour and test it on long runs.
- Run the first 5 km 5–10 s/km slower than your goal pace.
Article contents
Running 21.1 kilometres is a big step: fitness alone is no longer enough — you need to build endurance, learn to pace yourself and fuel properly during the race. The good news is that with 12 weeks and four runs a week, a runner who can already finish a 10K can prepare for a first half marathon with room to spare.
Before you start: are you ready for a half marathon?
This plan assumes that, before week 1:
- You run regularly 3–4 days a week, about 20–25 km in total.
- You can run 8–10 km non-stop at a comfortable pace.
- You are not carrying an injury.
If you are not there yet, train for a 10K first with our 8-week plan: it is the best springboard to 21K.
The three keys to half marathon training
1. The long run
It is the most important session. It grows from 10 to 18 km over the plan, always at an easy pace: you should be able to hold a conversation. Its job is to get your legs, heart and energy systems used to efforts of almost two hours. You don’t need to run the full 21 km before race day; the taper and the race-day atmosphere carry you through the last few kilometres.
2. Threshold work
Blocks at threshold pace — “comfortably hard”, the effort you could hold for about an hour — do the most to improve your ability to sustain a pace for a long time. They are demanding but controlled: you should not finish exhausted.
3. Half marathon pace
From week 7, sections at your goal pace appear. They check that your goal is realistic and let your body recognise that pace on race day without having to think about it.
12-week half marathon training plan
Four runs a week. Arrange them so the quality session and the long run don’t fall on consecutive days; for example: Tuesday easy, Thursday quality, Friday easy and Sunday long run. Quality sessions start with 2–3 easy kilometres and end with 1–2 km of jogging, already included in the figure.
| Week | Easy | Quality | Easy | Long run | Total |
|---|---|---|---|---|---|
| 1 | 6 | 6: 8 × 1 min fartlek | 5 | 10 | 27 |
| 2 | 6 | 7: 4 × 1 km at 10K pace | 5 | 11 | 29 |
| 3 | 7 | 7: 2 × 10 min at threshold | 5 | 12 | 31 |
| 4 (recovery) | 5 | 6: 6 strides | 5 | 10 | 26 |
| 5 | 7 | 8: 5 × 1 km at 10K pace | 6 | 13 | 34 |
| 6 | 7 | 8: 3 × 10 min at threshold | 6 | 14 | 35 |
| 7 | 7 | 9: 6 km at half marathon pace | 6 | 16 | 38 |
| 8 (recovery) | 6 | 7: 6 strides | 5 | 12 | 30 |
| 9 | 8 | 9: 2 × 15 min at threshold | 6 | 17 | 40 |
| 10 | 8 | 10: 7 km at half marathon pace | 6 | 18 | 42 |
| 11 | 6 | 8: 3 × 2 km at half marathon pace | 5 | 13 | 32 |
| 12 (race) | 5 | 5: 4 strides | Rest | Half marathon | — |
Weeks 4 and 8 reduce the volume so you can absorb the work; weeks 11 and 12 are the final taper: fewer kilometres, a little pace to stay sharp, and fresh legs on the start line.
Half marathon fueling and hydration
In a race lasting more than an hour and a quarter, glycogen stores start to matter. Common sports nutrition guidance for efforts of 1 to 2.5 hours is 30 to 60 grams of carbohydrate per hour — one or two gels per hour, depending on the brand.
- Practise on your long runs. Your stomach needs training too. Try your gels from the 14 km long runs onwards.
- First gel around minute 40–45, then every 30–40 minutes, always with a little water.
- Drink to thirst at the aid stations. In heat and humidity, add electrolytes; drinking too much is not a good idea either.
- The night before, a normal dinner with plenty of carbohydrate and little fat and fibre. There is no need for a big “carb load”.
Race-day strategy
Split the race into three parts. For the first 5 km, hold back: run 5–10 seconds per kilometre slower than your goal pace even if you feel amazing. From km 5 to 16, settle into your pace. The last 5 km are for whatever you have left.
Bear in mind that your watch will probably show more than 21.1 km: the official course is measured along the shortest line and you won’t always follow it. So it pays to aim for a watch pace slightly faster than the exact maths suggests. We explain it in detail in our running pace guide, where you can also estimate your half marathon time from your 10K.
Frequently asked questions
How many weeks do you need to train for a half marathon?
If you can already run a 10K comfortably, 10 to 12 weeks. Starting from a smaller base, add 6 to 8 weeks beforehand to increase your volume gradually.
How many kilometres a week should I run for a half marathon?
To finish feeling good, most beginner plans peak at 35–45 km in the heaviest weeks. What matters is getting there gradually.
Do you need to run 21 km before the race?
No. With long runs of 16 to 18 km your body is ready; the taper in the final weeks and the race atmosphere carry you the rest of the way.
How many gels should I take in a half marathon?
For most runners, one to three depending on finish time: the first around minute 40–45 and then every 30–40 minutes. Test them on your long runs first.
We write practical training guides with the same logic the app uses: measure first, assume nothing.
This content is for information only and does not replace advice from a doctor or coach. If you have an injury or a heart condition, or have not exercised in a while, check with a professional before starting a plan.
