Categories / Running & athletics
Half Marathon Training
12-16 week build to 21 km.
How to start
Be comfortable running 10 km before you begin. A typical plan uses three to four runs a week for 12 weeks, with a long run that grows toward 16 to 19 km.
How to progress
Grow the long run every week or two, with an easier week every fourth week, and taper in the last two weeks before the race.
What the evidence says
Evidence: limited
We found no trials comparing half-marathon plans. A 2025 study of US marathons and half-marathons found cardiac arrest in 0.54 per 100,000 finishers, and a falling case fatality rate, so serious cardiac events are rare. The broader training-injury research is mixed: the evidence linking weekly distance or sudden jumps to injury is conflicting.
Take care: A longer distance means a longer recovery. Build the long run gradually and check with a GP before you start if you have a heart condition or high blood pressure.
Sources
12-week starter plan
Start once you can run 10 km comfortably. Three or four runs a week, with a long run that grows. Week 12 is race week.
Tick each week as you finish it; your ticks are saved on this device only. Repeat a week if it felt hard. Weeks 4, 8 and 12 hold steady so you can settle. This is a general plan, not medical advice.
Add reminders to your calendar
Pick your days and time. You will download a calendar file that adds 12 weeks of reminders to Google, Apple or Outlook calendar.
Calories and weekly minutes
Enter your details for a rough estimate. Based on about 9.5 METs (Steady running (about 6 mph)). Real figures vary by 20% or more between people.
Tips and common mistakes
Tips
- Take on fluid and energy on long runs and practise it before race day.
- Run your long run at an easy, talking pace.
- Rest properly in the final fortnight.
Common mistakes
- Running the long run too fast.
- Not practising race-day nutrition.
- Adding distance and speed in the same week.
Kit and cost
Moderate Approximate UK prices.
- Well-fitted running shoes (about £80 to £150)
- A running watch (about £100 to £300), optional
- Energy gels or chews for long runs (about £1.50 each)
- Race entry (about £30 to £60)
Frequently asked questions
How long should I train for a half marathon?
Around 12 weeks if you can already run 10 km comfortably.
How far should I run in training?
Many plans peak at 16 to 19 km. You do not need to run the full 21 km before the race.
Is a half marathon safe?
For healthy people, serious events are rare. In a 2025 US study, cardiac arrest occurred in around 1 in 185,000 finishers.
What if I miss a week of training?
Do not cram. Pick up from where you left off, or step back a week.
Good for: Heart & fitness Endurance
Compare with similar options
| Half Marathon Training | Interval Running (Fartlek) | Trail Running | Cross Country Running | |
|---|---|---|---|---|
| Typical session | 60 min × 4/wk | 40 min × 2/wk | 60 min × 2/wk | 45 min × 2/wk |
| Effort | ●●●●○ | ●●●●○ | ●●●●○ | ●●●●○ |
| Cost | Low cost | Low cost | Low cost | Free |
| Equipment | No equipment | No equipment | Basic kit | Basic kit |
| Impact | High impact | High impact | Medium impact | Medium impact |
| Fitness needed | Moderate fitness | Moderate fitness | Moderate fitness | Moderate fitness |
| Evidence | limited | moderate | limited | limited |