12-Week 70.3 Beginner Training Plan: Your First Half-Ironman

Plan Overview

This 12-week plan is designed for beginner to lower-intermediate triathletes targeting their first 70.3 (half-ironman distance) event: 1.9km swim, 90km bike, and 21.1km run. You should be comfortable completing an Olympic distance triathlon before starting this plan, and ideally have completed a full triathlon season. By the end of week 12, you will have the aerobic endurance, pacing discipline, and race-day confidence to complete a 70.3 in 5 to 7 hours.

Prerequisites

• Can swim 1500m continuously (pool or open water)
• Can ride 60km outdoors comfortably
• Can run a half marathon (or at least 15km) without stopping
• Has completed at least one Olympic distance triathlon
• Access to a pool, open water venue, road bike or turbo trainer, and running routes
• Available training time: 8 to 12 hours per week (peak weeks reach 14 hours)

Plan Structure

The plan follows a four-phase structure with a progressive overload model. Volume builds gradually over 10 weeks before a meaningful two-week taper that allows full recovery and race-readiness going into your event.

• Weeks 1 to 3: Base Phase — Establishing consistent training habits, building aerobic endurance across all three disciplines. Average 8 to 9 hours per week. Focus on technique and aerobic volume at Zone 2 effort.
• Weeks 4 to 7: Build Phase — Increasing long session distances. Introduction of threshold work in swim and run. Brick sessions begin. Average 10 to 11 hours per week.
• Weeks 8 to 10: Peak Phase — Longest sessions of the plan. Race-pace efforts integrated into bike and run. 90km ride and half-marathon-distance run completed in separate sessions. Average 12 to 14 hours per week.
• Weeks 11 to 12: Taper — Volume drops by 40 to 50%. Intensity maintained with short sharpeners. Focus on rest, race-day logistics, and nutrition rehearsal.

Sample Week (Build Phase — Week 5)

This is a representative mid-plan week to give you a sense of the training load and session variety.

• Monday: Rest or 20-minute easy walk
• Tuesday: Pool swim — 2km with technique drills and CSS pace sets (50 to 60 minutes)
• Wednesday: Turbo trainer sweet spot ride — 60 minutes at 88 to 93% FTP
• Thursday: Threshold run — 45 minutes with 3 x 8 minutes at 10K pace
• Friday: Recovery swim — 1.5km easy with drills (40 minutes)
• Saturday: Long outdoor ride — 70km at aerobic pace with nutrition practice
• Sunday: Bike-run brick — 45 minutes easy spin followed by 20-minute run at race-pace feel

Key Tips for Success

• Consistency beats heroics: Missing one session matters far less than the cumulative effect of 12 weeks of steady training. Do not try to make up missed sessions by doubling up — just resume the plan.
• Practise race nutrition every long session: Your body needs to be trained to absorb 60 to 75g of carbohydrate per hour on the bike. Start trialling your race-day nutrition products in week 3.
• Run off the bike: The brick session on Sundays is non-negotiable. The transition from cycling to running recruits different muscles and requires specific adaptation — you cannot simulate this on a turbo.
• Taper with confidence: Reduced volume in weeks 11 and 12 is intentional. The fitness is banked — trust the process and resist the urge to add extra sessions.