Running a Half Marathon for the First Time: What to Expect

Photo by Stephen Leonardi on Pexels

A half marathon (21.1km / 13.1 miles) is the most popular long-distance race in the UK. It’s genuinely demanding — not something you finish on base fitness alone — but it’s achievable for any runner who can currently cover 5–6 miles and is willing to commit to 12–16 weeks of structured training.

First-timers often don’t know what to expect from the training process, the race itself, or how their body will respond. This guide covers all three.

Is a Half Marathon Right for You Now?

You’re ready to start half marathon training if:
– You can currently run 5–6 miles (8–10km) without stopping
– You’ve been running consistently for 3–6+ months (not just recently)
– You’re not currently carrying a running injury

If you can’t yet run 5–6 miles, complete a 10K training plan first. Attempting a half marathon plan without the base fitness typically leads to injury within weeks 4–8.

Training: What 12 Weeks Actually Looks Like

A half marathon plan for beginners typically involves:
– 3–4 runs per week
– A long run that builds gradually from around 8 miles to 12 miles by peak week
– Easy runs during the week to accumulate mileage
– One quality session (tempo run or race-pace miles) per week from week 5 onward

The long run is the cornerstone. It builds from 8 miles to 11–12 miles over the training period. Everything else is support for this session. Missing long runs is what derails most half marathon campaigns.

Weekly mileage progression (approximate):
– Weeks 1–3: 20–25 miles
– Weeks 4–7: 25–32 miles
– Weeks 8–11: 30–40 miles
– Week 12 (taper): 15–20 miles

The taper (reducing mileage in the final 10–14 days before the race) is important and counterintuitive. Many first-timers panic during the taper because they feel like they’re losing fitness. They’re not — they’re arriving at the start line fresh.

Pacing: The Most Important Decision

First-time half marathon pacing mistakes are almost universal — everyone goes out too fast in the first 3–4 miles because the crowd and adrenaline make a faster pace feel easy. The consequences arrive around miles 8–10.

The right approach:
– Start at slightly slower than your target race pace for the first 3 miles
– Run at target pace for miles 3–10
– Use whatever you have left for miles 10–13

A useful rule: if you feel strong at mile 10, you paced it right. If you feel strong at mile 5, you went out too fast.

For a first half marathon, running by effort rather than exact pace is often more reliable — keep effort at “comfortably hard” (you can speak in short phrases but not hold a conversation) and let the pace be what it is.

Estimated finish times:

These are estimates — first half marathons often run slightly slower than the formula suggests because race nerves, pacing errors, and nutrition issues all take experience to manage.

Nutrition on the Day

A half marathon typically takes 1.5–3 hours. You need to fuel during the race.

Before the race: Eat a familiar breakfast 2.5–3 hours before the start — porridge, toast, banana. Nothing new, nothing heavy.

During the race: 1 gel or equivalent every 45–50 minutes. Most first-time half marathons are well-served by two gels — one at mile 4–5 and one at mile 9–10. Practice with gels in training before race day.

Water: Take water at every aid station from mile 3 onward. Don’t gulp — small sips while running or walking briefly through stations.

What Miles 10–13 Feel Like (For Honesty)

The last 3 miles of a first half marathon are typically harder than training prepared you for. This is partly physical (glycogen depletion, muscular fatigue) and partly psychological — you know you’re close but the finish still seems far.

Things that help:
– Having fuelled well throughout
– Breaking it into chunks (“just get to mile 11, then reassess”)
– The crowd noise at the finish, which is a genuine physiological accelerant for most runners

Things that don’t help:
– Thinking about the total distance still to cover
– Looking at your watch obsessively
– Stopping (walking is fine for a minute; stopping makes it harder to restart)

What to Expect After the Finish Line

• First few minutes: The combination of relief, endorphins, and physical exhaustion is overwhelming for most first-timers. Expect to feel emotional, shaky, and desperate for water.
• Getting your medal: Take the photo. You earned it.
• Days 1–3 after: DOMS (delayed onset muscle soreness) peaks around 24–48 hours post-race. Stairs will be problematic. Walking downstairs backwards is a genuine strategy employed by serious runners. This is normal and passes.
• Return to running: Wait at least 7–10 days before easy running again. A half marathon is significantly more tissue-damaging than a training run and full recovery takes longer than it feels like it should.

Summary

Your first half marathon is a milestone worth preparing properly for:

1. You need to be running 5–6 miles before starting the training plan — attempting it without the base leads to injury
2. The long run is the most important session — don’t skip it; everything else in the plan supports it
3. Go out slower than you feel like in the first 3 miles — the race is won in miles 10–13, not miles 1–3
4. Take 2 gels during the race — practice with them in training first
5. Rest properly afterward — 7–10 days before easy running; a half marathon takes real recovery

Next read: How to train for a 10 mile race: complete guide