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A half marathon — 13.1 miles or 21.1km — is the most popular race distance in the UK and one of the best first-race choices for runners who’ve outgrown 5K and 10K. It’s long enough to require real training but short enough that the training doesn’t dominate your life.
This 12-week plan assumes you can already run 5K continuously. If you’re not there yet, complete a Couch to 5K programme first and build a few weeks of consistent easy running before starting.
Before You Start: Prerequisites
- Can run 5K continuously at easy pace
- Have been running consistently for at least 4–6 weeks
- Running 3 times per week already
- No current injury
If you’re starting from a lower base, add 4 weeks of building to 30–35km/week before beginning Week 1.
How the Plan Works
4 days per week: Long run, two easy runs, one quality session.
The long run is the centrepiece: It builds the endurance base that lets you cover 21km on race day. It should always feel comfortable — conversational pace, never pushing.
The quality session: Once a week, a tempo run or intervals. These build speed and running economy. Keep these genuinely hard (tempo = comfortably hard; intervals = hard).
Easy runs: The remaining two runs are genuinely easy — conversational pace. Most runners run these too fast. Slow down.
Recovery weeks: Weeks 4, 8, and 12 are reduced-volume recovery weeks. Don’t skip them.
The 12-Week Plan
Week 1
– Tue: 30 min easy
– Thu: 4 × 5 min tempo with 2 min recovery
– Sat: 30 min easy
– Sun: Long run 8km (easy pace)
Week 2
– Tue: 35 min easy
– Thu: 5 × 5 min tempo with 90 sec recovery
– Sat: 30 min easy
– Sun: Long run 10km
Week 3
– Tue: 35 min easy
– Thu: 3 × 10 min tempo with 2 min recovery
– Sat: 35 min easy
– Sun: Long run 12km
Week 4 (Recovery)
– Tue: 25 min easy
– Thu: 20 min easy + 4 strides
– Sat: 25 min easy
– Sun: Long run 8km
Week 5
– Tue: 40 min easy
– Thu: 6 × 800m at 10K effort, 90 sec recovery
– Sat: 35 min easy
– Sun: Long run 14km
Week 6
– Tue: 40 min easy
– Thu: 4 × 10 min tempo with 2 min recovery
– Sat: 35 min easy
– Sun: Long run 16km
Week 7
– Tue: 40 min easy
– Thu: 5 × 800m at 10K effort, 90 sec recovery
– Sat: 35 min easy
– Sun: Long run 18km
Week 8 (Recovery)
– Tue: 30 min easy
– Thu: 25 min easy
– Sat: 25 min easy
– Sun: Long run 12km
Week 9
– Tue: 40 min easy
– Thu: 35 min tempo continuous
– Sat: 35 min easy
– Sun: Long run 18km
Week 10
– Tue: 40 min easy
– Thu: 6 × 800m at 10K effort, 90 sec recovery
– Sat: 35 min easy
– Sun: Long run 20km (this is your peak long run)
Week 11
– Tue: 35 min easy
– Thu: 30 min tempo
– Sat: 30 min easy
– Sun: Long run 16km
Week 12 (Taper)
– Tue: 25 min easy + 4 strides
– Thu: 20 min easy + 3 × 5 min at race pace
– Sat: 15 min very easy shake-out jog
– Sun: RACE DAY
Race Pace and Finish Time Expectations
Your race pace should be slower than tempo effort — the half marathon is a sustained aerobic effort, not a sprint.
A rough guide based on your current 5K time:
| 5K time | Predicted half marathon time |
|---|---|
| 25:00 | ~1:55–2:05 |
| 28:00 | ~2:10–2:20 |
| 32:00 | ~2:25–2:40 |
| 36:00 | ~2:45–3:00 |
These are estimates — individual variation is significant. Use your tempo run pace as a guide: race pace will be approximately 10–15 seconds per km slower than your continuous 30-minute tempo pace.
Nutrition and Fuelling
For runs under 75 minutes, water is sufficient. For runs over 75 minutes, you need carbohydrate:
Energy gels: Easiest option. Take one gel every 40–45 minutes during the race. Practice with your chosen gel brand in training — don’t use something new on race day.
Chews or dates: Some runners prefer real food. Medjool dates work well for moderate-intensity running.
Race day breakfast: 2–3 hours before the start. Oats, toast with peanut butter, or banana — something familiar, high carb, low fibre.
What to Do When You Miss Sessions
Life happens. Don’t try to make up missed sessions by doubling up — just continue with the plan as scheduled. Missing one session in a 12-week plan has minimal impact on race readiness.
If you miss a week due to illness or injury: return at the last completed week’s mileage level, not where you left off.
Race Day Tips
Start slower than feels right: The most common half marathon mistake is going out too fast in the first 3km. The race is 21km — patience in the first third means energy for the last.
Walk through aid stations: Taking water is easier when walking; you’ll lose less to spillage and recover better from drinking on the move.
Mental markers: Break the race into thirds. The first 7km: settle and feel comfortable. The middle 7km: maintain pace, focus on form. The last 7km: everything you have left.
Summary
First half marathon in 12 weeks:
- The long run is the most important session — never miss it; never run it fast
- Taper properly in Week 12 — less is more in the final week; trust the training
- Practice fuelling in training — use gels or chews on your long runs over 75 minutes to learn how your stomach handles them
- Start the race conservatively — first 5km should feel almost too easy; you’ll be grateful in kilometre 18
- Finish time doesn’t matter for your first half marathon — finishing is the goal; a time target comes in the second race