Quick summary
- Who it's for: runners who can comfortably run 10 km and currently run 20–25 km a week on three or four days.
- The plan: 10 weeks, peaking at about 40 km a week with an 18–20 km long run.
- The key change: the long run grows by 1–2 km a week, with a lighter week every fourth week.
- Pace rule: most running is easy; one quality session a week builds speed endurance.
- Race tip: start the first 5 km slightly slower than goal pace, then settle in.
Moving from 10K to the half marathon is one of the most satisfying steps in running. The distance doubles, but the jump is very manageable if you build your long run gradually and keep most of your running easy. This 10-week plan gets you to the start line ready to finish strong.
Are you ready?
Start this plan if you can tick most of these:
- You can run 10 km without stopping, at any pace.
- You currently run 20–25 km a week, on three or four days.
- You've been running consistently for at least three months.
- You've had no injury that stopped you running in the last six weeks.
If you're not quite there, spend three or four weeks building easy running to 20 km a week first.
Your training paces
Use effort first and pace second. Find your goal half-marathon pace in our half marathon pace chart.
- Easy: conversational, roughly 60–90 seconds per km slower than half-marathon pace. Most of your running.
- Long run: comfortable and steady, 45–75 seconds per km slower than half-marathon pace.
- Half-marathon pace (HMP): comfortably hard; you can say a few words.
- Threshold: a little faster than HMP, roughly your 15K to 10-mile race effort.
- 10K effort: hard but controlled, for short repeats.
The 10-week plan
Each week has three key runs. Add one easy run of 30–40 minutes if you're running four days a week.
| Week | Weekly km | Quality session | Steady run | Long run |
|---|---|---|---|---|
| 1 | 22 | 6 × 2 min at 10K effort, 2 min jog | 5 km easy | 10 km |
| 2 | 25 | 3 × 6 min threshold, 2 min jog | 6 km easy | 11 km |
| 3 | 28 | 5 × 3 min at 10K effort, 2 min jog | 6 km with last 2 km at HMP | 13 km |
| 4 | 24 | 6 × 20 s strides after an easy run | 5 km easy | 11 km (recovery week) |
| 5 | 31 | 2 × 10 min threshold, 3 min jog | 7 km with 3 km at HMP | 14 km |
| 6 | 34 | 6 × 3 min at 10K effort | 8 km with 4 km at HMP | 16 km |
| 7 | 37 | 3 × 8 min threshold | 8 km with 5 km at HMP | 17 km |
| 8 | 40 | 5 × 1 km at 10K effort | 9 km with 6 km at HMP | 18–20 km |
| 9 | 30 | 3 × 5 min threshold | 6 km with 3 km at HMP | 13 km |
| 10 | 15 + race | 4 × 1 km at HMP on Tuesday | 4 km easy with strides | Half marathon |
Week 4 and week 9 are deliberately lighter. Recovery weeks are when your body absorbs the training.
Why the long run matters most
The long run is what turns a 10K runner into a half-marathon runner. It strengthens your heart, muscles, tendons and bones for the extra distance, teaches your body to use fat as fuel, and gives you a chance to practise pacing, fueling and kit.
Keep it easy. If you finish a long run unable to run for three days, it was too fast. Our guide to long-run pace explains why slower long runs build more fitness.
Fueling and kit for 21 km
- Fuel: for runs over about 75 minutes, practise taking a gel or sports drink around 40–50 minutes in. On race day, one or two gels is plenty for most runners.
- Fluid: drink to thirst, more in warm conditions.
- Kit: test your race shoes, socks and top on your 16–20 km long runs. Chafing that never appeared over 10 km often shows up after 15 km. See how to stop chafing on long runs.
Race-day strategy
- Kilometres 1–5: 3–5 seconds per km slower than goal pace. It should feel easy.
- Kilometres 5–15: settle into goal pace and stay relaxed.
- Kilometres 15–19: focus on form and rhythm; this is the hardest stretch.
- The last 2 km: push.
FAQ
How long does it take to go from 10K to half marathon?
Most runners who can comfortably run 10 km need about 8–12 weeks to prepare for a half marathon. This plan takes 10 weeks.
How long should my longest run be before a half marathon?
A longest run of 18–20 km is ideal for most runners, done two or three weeks before the race. Some runners prefer to run the full 21 km in training, but it isn't necessary.
How many days a week should I run for a half marathon?
Three to four days a week is enough for most first-time half marathoners, with one long run, one quality session and one or two easy runs.
Can I run a half marathon after training for 6 weeks?
If you're already running 25–30 km a week with a long run of 12–14 km, six weeks can be enough to finish. If you're starting from a 10K base, 8–12 weeks is safer.
What pace should I run my first half marathon?
Start a little slower than you think you can manage, around your comfortable long-run pace or slightly faster, and pick it up in the second half if you feel good. Finishing strong is a better first goal than a specific time.
This article is general training information, not medical advice. Check with a doctor before starting a new training programme, especially if you have a health condition.