How to Train for Your First Half Marathon: A 12-Week Plan
Runward —
21.1 km is the distance where preparation stops being optional. You can improvise a 10K. A half marathon exposes every gap in your endurance, fuelling and pacing.
Where you should start
Comfortably running 8–10 km and covering 20–25 km a week is the right launch point. If you are below that, spend a month building easy mileage before starting the plan below.
What the training has to build
- Aerobic endurance — from the weekly long run.
- Sustained speed — from tempo running at close to half marathon effort.
- Efficiency — from strides, intervals and strength work.
- Fuelling practice — most runners need 30–60 g of carbohydrate per hour beyond 75 minutes.
Find your Pace
Turn your goal half marathon time into per-kilometre targets for the tempo, interval and long-run sessions in the plan below.
The 12-week plan (4 runs per week)
| Week | Tempo / interval | Long run | Weekly total |
|---|---|---|---|
| 1 | 20 min tempo | 10 km | ~28 km |
| 2 | 5 × 800 m at 5K pace | 12 km | ~31 km |
| 3 | 2 × 12 min tempo | 14 km | ~34 km |
| 4 | 25 min tempo | 10 km (easier) | ~28 km |
| 5 | 4 × 1 km at 10K pace | 15 km | ~37 km |
| 6 | 30 min tempo | 16 km | ~40 km |
| 7 | 3 × 2 km at half pace | 12 km (easier) | ~34 km |
| 8 | 2 × 15 min tempo | 18 km | ~43 km |
| 9 | 6 × 1 km at 10K pace | 19 km | ~45 km |
| 10 | 40 min tempo | 16 km with last 5 km at goal pace | ~42 km |
| 11 | 20 min tempo | 12 km | ~30 km |
| 12 | 4 × 400 m at 5K pace | Race day | ~20 km |
Keep every other run genuinely easy. The plan only works if the easy days are easy.
Long run rules
- Run it 60–90 seconds per km slower than goal race pace.
- Build the longest run to 18–19 km. You do not need to run 21 km in training; race-day adrenaline covers the difference.
- Practise your race breakfast, race shoes, and your gels on the long run — never for the first time on race day.
Fuelling and hydration
Beyond 75 minutes, take one gel every 35–45 minutes with water. Drink to thirst; in hot, humid conditions plan 400–700 ml per hour and add electrolytes. Test this in weeks 8–10 so nothing on race day is new.
The taper
Reduce volume by 25% in week 11 and 40–50% in week 12 while keeping short, sharp intensity. Tapering feels wrong — heavy legs, restlessness, phantom niggles — and it still works. Fitness is built weeks earlier; the taper simply lets it surface.
Race-day pacing for 21.1 km
Run the first 5 km 5–10 seconds per km slower than goal pace, settle into goal pace from 5 to 15 km, then decide at 15 km whether you have anything left. Runners who negative-split their first half marathon almost always beat runners who went out fast, even with identical fitness.
Common first-timer mistakes
- Racing every training run.
- Skipping strength work, then developing calf or knee pain in week 8.
- Adding long-run distance more than 2 km per week.
- Chasing a goal time set by someone else's finish line photo.
Let the data set your goal
Runward builds your half marathon plan around your target date, predicts your realistic finish time from your recent training, and shows the weekly load, pace and heart-rate trends behind that prediction. When you miss a week or add unplanned races, the plan adapts instead of quietly becoming wrong.