Half Marathon Training Plan: From 10K to 13.1 Miles in 12 Weeks

The half marathon is, for many runners, the perfect challenge. It's long enough to demand serious preparation, but not as punishing as a full marathon. If you can already run 10K with reasonable comfort, you're just 12 weeks away from crossing the finish line of your first 21K (World Athletics).

This plan is designed for runners who already have a base of at least 25-30 km (15-19 miles) per week and can finish 10K without issues. You don't need to be fast -- just consistent.

Prerequisites before you start

Before jumping into half marathon training, make sure you tick these boxes:

• You run at least 3-4 days per week on a regular basis (minimum 2-3 months)
• You can finish 10K without stopping and without joint pain
• Your weekly volume is at least 25-30 km (15-19 miles)
• You don't have any active injuries or chronic pain that worsens when you run

If you're not quite there yet, we recommend completing our 10K training plan first and then coming back here (ACSM).

Plan structure: 3 phases

The 12-week plan is divided into three 4-week phases. Each phase has a specific goal:

Week-by-week schedule

Each week includes 4-5 sessions. Rest days are flexible -- feel free to move them around based on your schedule. The key is not to stack two quality sessions on back-to-back days.

Week	Mon	Tue	Wed	Thu	Fri	Sat	Sun	Total km
1	Rest	6 km easy	7 km w/ 4x1' fast	Rest	6 km easy	5 km easy	12 km long	36
2	Rest	7 km easy	7 km w/ 5x1' fast	Rest	6 km easy	5 km easy	13 km long	38
3	Rest	7 km easy	8 km w/ 3x5' tempo	Rest	7 km easy	5 km easy	14 km long	41
4	Rest	6 km easy	6 km easy	Rest	5 km easy	Rest	10 km easy	27
5	Rest	7 km easy	9 km w/ 4x1km intervals	Rest	7 km easy	5 km easy	15 km long	43
6	Rest	8 km easy	9 km w/ 20' tempo	Rest	7 km easy	5 km easy	16 km long	45
7	Rest	8 km easy	10 km w/ 5x1km intervals	Rest	7 km easy	6 km easy	17 km long	48
8	Rest	6 km easy	7 km easy	Rest	5 km easy	Rest	12 km easy	30
9	Rest	8 km easy	10 km w/ 25' tempo	Rest	7 km easy	5 km easy	18 km long	48
10	Rest	8 km easy	9 km w/ 3x2km intervals	Rest	7 km easy	5 km easy	19 km long	48
11	Rest	7 km easy	8 km w/ 15' tempo	Rest	6 km easy	5 km easy	14 km long	40
12	Rest	5 km easy	5 km w/ 3x3' race pace	Rest	4 km easy	Rest	RACE DAY 21K	35

Session types explained

Easy run

Your bread and butter. A comfortable pace where you can hold a conversation without gasping. This should make up 70-80% of your weekly training. If you use a heart rate monitor, stay in zone 2. Don't worry about pace -- the key is that it feels easy (research studies).

Tempo run

"Comfortably hard" pace: you can say short sentences but can't keep up a conversation. This is your threshold pace -- roughly the effort you could sustain for 1 hour in a race. It improves your ability to hold a steady pace for longer.

Intervals

Repetitions of 1-2 km at a fast pace (faster than race pace) with recovery between them (1-2 minutes easy jog). They improve your VO2max and running economy. Always warm up for 10-15 minutes beforehand (British Journal of Sports Medicine).

Long run

The star session of the plan. Run at an easy pace (even slower than your regular easy runs) with the goal of accumulating time on your feet. This is where your body learns to use fat as fuel and your legs adapt to repeated impact. Never run this one fast.

Fartlek

Unstructured pace changes during an easy run. For example, "1 minute fast, 1 minute easy" repeated several times. It's the most fun way to add quality without the pressure of track intervals.

Half marathon nutrition

After 60-75 minutes of running, your glycogen stores start to run low. For a half marathon, you need a nutrition plan:

• Before: Have breakfast 2-3 hours before the race with easy-to-digest carbs (toast, banana, jam). Nothing new on race day.
• During: One gel every 30-45 minutes starting from the 8-10 km mark. SiS isotonic gels are ideal because they don't need water. Practice during your long training runs.
• Hydration: Drink at aid stations, but don't overdo it. Isotonic drinks like Isostar provide electrolytes along with fluids.
• After: Protein + carbs within the first 30-60 minutes post-race to kickstart muscle recovery.

Check out our complete guide to energy gels to pick the best ones for you.

Race day tips

1. Don't debut anything: Not shoes, not a shirt, not gels. Everything should be tested in training first.
2. Start conservative: For the first 5 km you should feel like you're going too slow. The right pace is the one you can sustain for the full 21K, not the one you feel like running in the first 3.
3. Break the race into thirds: The first 10K with your head, the next 10K with your legs, the last kilometer with your heart.
4. Respect the aid stations: Stop, drink, take your gel. Losing 10 seconds is better than getting dehydrated.
5. Enjoy it: This is your first half marathon. It's not an exam -- it's a celebration of all the work you've put in over these 12 weeks.

Common half marathon training mistakes

• Running your long runs too fast. The goal is distance, not speed. If you're wrecked the next day, you went too hard.
• Skipping recovery weeks. Your body improves during rest, not during training. Weeks 4 and 8 are sacred.
• Increasing volume too quickly. The 10% rule exists for a reason. Overuse injuries are the number one cause of dropping out.
• Ignoring nutrition. Practicing gel and isotonic drink intake during long runs is just as important as training your legs.
• Skipping strength work. Two 20-minute strength sessions per week (squats, lunges, planks) dramatically reduce your injury risk.
• Running while sick or injured. Missing a workout won't ruin a plan. Running through an injury can ruin your entire season.

Frequently asked questions

How long do I need to train for a half marathon?

If you can already run 10K comfortably, 12 weeks is an ideal timeframe. If you have less of a base, consider 16-20 weeks. The key is not to skip phases and to respect your rest days.

How many days a week should I train?

Between 4 and 5 days is optimal for this plan. You need at least 2 days of rest or cross-training (cycling, swimming, yoga) so your body can absorb the training.

Do I need to run 21K in training?

No. The longest run in the plan reaches 18-19 km (about 11-12 miles). Your body will have the capacity to cover the remaining distance on race day thanks to adrenaline, tapering and race-day logistics. Running the full distance in training only adds unnecessary fatigue.