12 Week Half Marathon Training Plan - This Messy Happy

Aug 13, 2025

Intro: This is a quick summary of 12 Week Half Marathon Training Plan from This Messy Happy. It’s a great watch — we’re breaking it down so you can try the workout today. Be sure to watch the full video for all the details.

Key Points:

Designed for casual runners who can already run about 5 km a few times a week and want to build to a half‑marathon in 12 weeks.
The plan uses three weekly runs (later four), a strength‑and‑conditioning session on Monday, and built‑in recovery weeks to avoid overuse injuries.
Training is split into three blocks:
1. Base block – gradually reach 7‑10 km easy runs.
2. Interval block – add short speed intervals while keeping mileage moderate.
3. Peak block – keep two steady runs and gradually increase the long weekend run; final week tapers.
Non‑negotiables: stretch after every session, do the strength‑conditioning workout each Monday, respect rest days and recovery weeks, and don’t miss two sessions in a row. Enjoy the process!

Workout Example:

Weeks 1‑4 (Base Block)
- Monday: Strength & conditioning (body‑weight circuit)
- Tuesday: Easy run 5–7 km (easy pace)
- Wednesday: Rest or cross‑train
- Thursday: Easy run 5–7 km
- Friday: Rest
- Saturday: Long run starting 7 km, add 1 km each week up to ~10 km
- Sunday: Rest or light activity

Weeks 5‑8 (Interval Block) – same structure, but replace the Tuesday run with a short interval session (e.g., 6 × 400 m at 5‑10 s faster than goal pace with 90 s jog recovery). Keep the weekend long run building to 12‑14 km.

Weeks 9‑12 (Peak & Taper) – keep two steady runs (5‑8 km) and a longer weekend run that peaks at 18‑20 km in week 11, then drop back 20‑30 % in week 12 for a fresh race day.