Half Ironman 70.3 Training Guide 2025: Complete 16-Week Plan for Your First or Fastest 70.3
Table of Contents
1. Introduction to Half Ironman 70.3
The Half Ironman 70.3 represents the perfect balance between an attainable endurance challenge and a genuinely demanding test of athletic ability. At 70.3 total miles—1.2-mile swim, 56-mile bike, and 13.1-mile run—this distance has exploded in popularity, with over 100 official Ironman 70.3 races held worldwide annually.
Whether you're stepping up from Olympic distance triathlons or this is your introduction to multi-sport racing, the 70.3 demands respect, preparation, and strategic execution. Unlike shorter races where you can rely heavily on fitness, the half Ironman requires mastery of pacing, nutrition, and mental toughness across 4-7 hours of racing.
Why 70.3 Is the Sweet Spot
Long enough to feel like a true endurance achievement, but manageable enough that you can train effectively with 10-12 hours per week. Recovery time is days rather than weeks, allowing you to race multiple 70.3s per season.
This guide provides everything you need to successfully complete—or crush—your Half Ironman. From building your aerobic engine to perfecting race-day nutrition, we'll cover the science-backed strategies that work for athletes at every level.
2. Understanding the 70.3 Distances
Before diving into training, let's understand what each discipline demands and how they contribute to your overall race performance.
| Discipline | Distance | % of Race Time | Typical Time Range |
|---|---|---|---|
| Swim | 1.2 miles (1.9 km) | 10-15% | 25-45 min |
| T1 | Swim to Bike | 1-2% | 2-8 min |
| Bike | 56 miles (90 km) | 50-55% | 2:15-3:30 |
| T2 | Bike to Run | 1% | 1-5 min |
| Run | 13.1 miles (21.1 km) | 30-35% | 1:30-2:45 |
Key Insights from the Numbers
The bike is king: With 50%+ of race time spent cycling, improvements here yield the biggest time gains. A 1 mph increase in bike speed saves more time than swimming 1:00/100m faster.
The run determines placement: While the bike takes the most time, the run is where races are won or lost. Athletes who ride too hard implode on the run; smart racers save enough for a strong half marathon.
The swim sets the tone: The swim is the smallest time factor but impacts your entire race. Exit the water calm, smooth, and with energy to spare. Going anaerobic in the swim affects bike power for the first 30+ minutes.
3. Fitness Assessment and Prerequisites
Not everyone should jump directly into Half Ironman training. Having baseline fitness in all three disciplines prevents injury and ensures you can handle the training load.
Recommended Prerequisites
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✓
Swimming: Can swim 1,000m continuously without stopping. Comfortable with bilateral breathing.
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✓
Cycling: Can ride 30+ miles comfortably. Familiar with shifting, group riding etiquette, and basic bike maintenance.
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✓
Running: Can run 6-8 miles at easy pace. No current running injuries.
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✓
Training History: 3-6 months of consistent training in at least one endurance sport.
Benchmark Tests
Use these tests to establish baseline fitness and track improvement during training:
| Test | Beginner Target | Intermediate Target |
|---|---|---|
| 1,000m Swim TT | Under 25:00 | Under 18:00 |
| 20-min FTP Test | 2.0+ W/kg | 2.8+ W/kg |
| 5K Run TT | Under 30:00 | Under 24:00 |
Calculate Your Training Zones
Use our FTP Calculator and Heart Rate Zone Calculator to establish accurate training zones for each discipline.
4. Training Structure and Periodization
A 16-week Half Ironman training plan typically follows a periodized structure that builds fitness systematically while preventing burnout and overtraining.
The Four Phases
Phase 1: Base Building (Weeks 1-4)
Focus on aerobic development and technique. Build volume gradually. Most workouts at Zone 2. Establish consistent training habits.
Weekly hours: 7-9
Phase 2: Build 1 (Weeks 5-8)
Introduce race-specific intensity. Add tempo and threshold work. Begin brick workouts. Increase long ride duration.
Weekly hours: 9-12
Phase 3: Build 2/Peak (Weeks 9-13)
Highest training volume and intensity. Race simulation workouts. Longest rides and runs. Practice race nutrition.
Weekly hours: 11-15
Phase 4: Taper (Weeks 14-16)
Reduce volume by 40-60%. Maintain intensity with shorter efforts. Focus on rest, nutrition, and race preparation.
Weekly hours: 5-8
Weekly Structure Template
A typical training week during the Build phase might look like this:
| Day | AM Session | PM Session |
|---|---|---|
| Monday | REST or Yoga | — |
| Tuesday | Swim: Technique + Intervals | Run: Easy |
| Wednesday | Bike: Intervals | Strength |
| Thursday | Swim: Endurance | Run: Tempo/Threshold |
| Friday | Bike: Easy Spin | REST |
| Saturday | Long Bike + Brick Run | — |
| Sunday | Long Run | Swim: Open Water (optional) |
5. Swim Training for 70.3
The swim is often the most daunting discipline for triathletes, yet it's where technique improvements yield the biggest returns. Unlike running or cycling, swimming faster is more about efficiency than fitness.
Key Swim Sessions
Technique Session (Weekly)
Focus on drills: catch-up, fingertip drag, single-arm, sighting practice. Keep distances short (25-50m) with full recovery. Video analysis helps identify flaws.
Threshold Set (Weekly)
Example: 8-10 x 100m at CSS pace (Critical Swim Speed) with 10-15 sec rest. Builds race-specific fitness and pacing awareness.
Endurance Swim (Build Phase)
Continuous swimming of 2,000-3,000m at moderate effort. Practice bilateral breathing and maintaining form when fatigued.
Open Water Preparation
Pool fitness doesn't automatically translate to open water competence. Plan for specific open water sessions:
- Sighting: Practice lifting your head every 6-8 strokes without breaking rhythm
- Drafting: Learn to swim on someone's hip or feet to save 10-25% energy
- Mass starts: Practice starting in groups, dealing with contact
- Beach starts/exits: Run-dive-swim and swim-stand-run transitions
- Wetsuit swimming: Different body position; practice before race day
Open Water Swimming Resource
For detailed open water techniques and race-day strategies, see our Open Water Swimming Complete Guide.
6. Bike Training for 70.3
The bike leg offers the greatest time-saving opportunity in triathlon. With 56 miles to cover, small improvements in power output, aerodynamics, or pacing strategy compound into significant gains.
70.3 Bike Power Targets
Racing the bike leg at the right intensity is crucial. Going too hard destroys your run; too easy leaves time on the table.
| Athlete Level | Target % of FTP | IF (Intensity Factor) |
|---|---|---|
| Beginner | 65-70% | 0.65-0.70 |
| Intermediate | 70-75% | 0.70-0.75 |
| Advanced | 75-80% | 0.75-0.80 |
| Elite | 80-85% | 0.80-0.85 |
Key Bike Workouts
Sweet Spot Intervals
2-3 x 20 min at 88-93% FTP with 5 min recovery. Builds sustainable power without excessive fatigue.
Race-Pace Ride
60-90 min steady at goal race watts (70-75% FTP). Practice holding consistent power regardless of terrain.
Long Ride
Build to 3.5-4 hours at Zone 2. Include race nutrition practice. One long ride should reach or exceed race distance.
VO2max Intervals (Build Phase)
5 x 4 min at 105-115% FTP with 4 min recovery. Raises ceiling fitness and improves recovery between efforts.
Know Your FTP
Accurate power zones are essential for 70.3 training. Test your FTP every 4-6 weeks using our FTP Calculator and generate a custom bike plan with our Cycling Training Plan Generator.
7. Run Training for 70.3
The 70.3 run is a half marathon—but after swimming 1.2 miles and cycling 56 miles. Your legs will be heavy, glycogen stores depleted, and mental fatigue high. Training must prepare you for this reality.
Running Off the Bike
Fresh half marathon pace and post-bike half marathon pace are very different. Expect to run 5-15% slower than your standalone half marathon time, depending on bike effort and fitness level.
The First Mile Rule
The first mile off the bike always feels terrible. Start 15-30 seconds per mile slower than goal pace. Your legs need 10-15 minutes to transition from cycling to running mechanics.
Key Run Workouts
Easy Runs (60% of run volume)
Zone 2 effort, conversational pace. Builds aerobic base without adding injury risk. Essential recovery between hard sessions.
Tempo Run
20-40 min at half marathon effort (Zone 3-4). Teaches you to hold "comfortably hard" pace. Key 70.3 race pace workout.
Long Run
Build to 12-14 miles (not full half marathon distance). Include some race-pace sections in the final miles.
Speed Work
6-8 x 800m at 10K pace with 90 sec jog recovery. Improves running economy and leg speed.
Run Volume Guidelines
Running creates the highest injury risk in triathlon. Build conservatively:
- Increase weekly mileage by no more than 10% per week
- Most athletes peak at 25-35 miles per week for 70.3
- Quality over quantity—3-4 well-designed runs beat 5-6 junk miles
- Include one rest or cross-training day after your longest run
8. Brick Workouts and Transitions
"Brick" workouts—back-to-back disciplines—are the secret weapon of triathlon training. They teach your body to switch between movement patterns and give you confidence for race day.
Why Bricks Work
- Neuromuscular adaptation: Your legs learn to run with cycling fatigue
- Mental preparation: Experiencing the "jelly legs" sensation removes race-day surprise
- Nutrition practice: Test fueling strategies across both disciplines
- Pacing calibration: Learn how hard you can bike and still run well
Sample Brick Progressions
| Phase | Bike | Run | Focus |
|---|---|---|---|
| Base | 45-60 min easy | 15-20 min easy | Adaptation |
| Build 1 | 90 min moderate | 30 min easy/mod | Endurance |
| Build 2 | 2.5-3 hr race effort | 45-60 min race pace | Race simulation |
| Peak | 3.5-4 hr race effort | 30-45 min race pace | Confidence |
Transition Practice
Transitions are the "fourth discipline." A slow T1 and T2 can cost 5+ minutes compared to a practiced athlete.
T1: Swim to Bike
- • Practice wetsuit removal while moving
- • Lay out gear systematically
- • Helmet on first, shoes optional (flying mount)
- • Target: Under 3 minutes
T2: Bike to Run
- • Shoes off before dismount line (elastic laces)
- • Rack bike, helmet off
- • Run shoes with elastic laces
- • Target: Under 2 minutes
9. 16-Week Training Plan Overview
This plan assumes you meet the fitness prerequisites and can dedicate 8-14 hours per week to training. Adjust volume based on your experience level and recovery capacity.
| Week | Phase | Swim | Bike | Run | Total Hrs |
|---|---|---|---|---|---|
| 1 | Base | 2x 2,000m | 2hr, 1hr easy | 3x 30-40min | 7-8 |
| 2 | Base | 2x 2,200m | 2.25hr, 1hr easy | 3x 35-45min | 8 |
| 3 | Base | 2x 2,500m | 2.5hr + brick | 3x 40-50min | 9 |
| 4 | Recovery | 2x 1,800m | 1.5hr easy | 2x 30min | 6 |
| 5 | Build 1 | 2x 2,500m (intervals) | 2.5hr, 1hr tempo | 3x 45min + tempo | 10 |
| 6 | Build 1 | 2x 2,800m | 3hr + brick | 3x 50min | 11 |
| 7 | Build 1 | 3x 2,500m | 3hr, 1.5hr intervals | 3x 55min + 8mi long | 12 |
| 8 | Recovery | 2x 2,000m | 1.5hr easy | 3x 35min easy | 7 |
| 9 | Build 2 | 3x 2,800m | 3.5hr + race brick | 3x 50min + 10mi | 13 |
| 10 | Build 2 | 3x 3,000m | 4hr endurance | 4x 50min + 11mi | 14 |
| 11 | Peak | 3x 3,000m (race sim) | 56mi race simulation | 3x 50min + 12mi | 15 |
| 12 | Recovery | 2x 2,200m | 2hr easy | 3x 40min | 8 |
| 13 | Peak | 3x 2,800m | 3.5hr + 45min brick | 3x 50min + 10mi | 12 |
| 14 | Taper | 2x 2,000m | 2hr, 1hr (some intensity) | 3x 40min | 8 |
| 15 | Taper | 2x 1,500m | 1.5hr, 45min | 3x 30min | 6 |
| 16 | Race Week | 2x 1,000m | 45min, 30min | 2x 20min + strides | 4 |
Generate Your Custom Plan
Get a personalized training plan based on your schedule and fitness level with our Triathlon Training Plan Generator.
10. Race Nutrition Strategy
Nutrition can make or break your 70.3. With 4-7 hours of racing, you'll need to consume significant calories while managing gut stress. The golden rule: nothing new on race day.
Pre-Race Nutrition
Race Week
- • Increase carbohydrate intake to 8-10g/kg body weight 2-3 days before
- • Reduce fiber intake 24-48 hours before to minimize GI issues
- • Stay well hydrated but don't overdo it (check urine color)
Race Morning (3-4 hours before)
- • 600-800 calorie breakfast: oatmeal, banana, toast, familiar foods
- • 16-24 oz water with electrolytes
- • Small snack 60-90 min before: banana, gel, or sports drink
During-Race Fueling
| Discipline | Calories/Hour | Fluid/Hour | Sodium/Hour |
|---|---|---|---|
| Swim | None | None | None |
| Bike | 200-300 | 20-30 oz | 500-1000mg |
| Run | 100-200 | 12-20 oz | 300-500mg |
Practical Fueling Strategy
Bike Nutrition Plan Example
For a 2:45 bike leg: 2 bottles (24 oz each) with 200 cal sports drink mix, plus 3 gels (300 cal total) taken at 45, 90, and 120 minutes. Total: ~700 calories on the bike.
The bike is your primary eating opportunity. Consume most calories here while your body is stable. On the run, switch to easily digestible options like gels, cola, or sports drink at aid stations.
Deep Dive on Endurance Nutrition
For comprehensive fueling strategies, carb-loading protocols, and gut training guidance, see our Nutrition for Endurance Athletes Complete Guide.
11. Race Day Execution
Race day is about executing your plan, not discovering what works. Every decision—pacing, nutrition, effort—should be practiced in training.
Race Morning Timeline
- 3-4 hours before: Wake up, eat breakfast
- 2-2.5 hours before: Arrive at venue, set up transition
- 1.5 hours before: Check bike (tires, brakes, gears, nutrition)
- 1 hour before: Put on wetsuit, begin warm-up
- 30 min before: Light swim warm-up (5-10 min)
- 15 min before: Final gel, find start position
Discipline-by-Discipline Strategy
The Swim
- • Start conservatively—avoid the washing machine if possible
- • Find your rhythm in the first 400m
- • Sight every 6-8 strokes to stay on course
- • Draft if you can find someone your pace
- • Calm yourself in the final 200m for a smooth T1
The Bike
- • Start eating/drinking within first 15 minutes
- • Ride your target watts, ignore other athletes
- • Stay aero but change positions periodically
- • Back off on climbs to save legs for the run
- • Increase effort slightly in final 5-10 miles if feeling good
The Run
- • First mile EASY—let your legs adjust
- • Walk through aid stations if needed (costs less than you think)
- • Break the run into segments (3 x 4.4 miles)
- • Expect a rough patch—it will pass
- • Negative split if possible: run the second half faster
Pacing Mistakes to Avoid
- Swimming too hard: Going anaerobic affects your bike for 30+ minutes
- Biking too hard early: "Feel good" watts in hour 1 become survival mode by hour 3
- Starting the run too fast: The adrenaline of T2 is deceiving—hold back
- Skipping nutrition: By the time you feel hungry, it's too late
Related Articles
Training for First Ironman Guide
Progress to full Ironman distance after 70.3 success
Olympic Triathlon Training Guide
Shorter distance for speed work and race practice
Zone 2 Training Complete Guide
Build the aerobic base essential for 70.3 success
Open Water Swimming Guide
Master the 1.2-mile swim with confidence
12. Frequently Asked Questions
How many hours per week do I need to train for a Half Ironman?
Most athletes training for a Half Ironman 70.3 should plan for 8-12 hours of training per week during the build phase, with peak weeks reaching 12-15 hours. Beginners may start with 6-8 hours and gradually increase. The key is consistency over volume—10 hours of quality training beats 15 hours of junk miles.
Can I finish a Half Ironman without swim training in open water?
While pool swimming builds fitness, open water practice is highly recommended. The challenges of sighting, drafting, mass starts, and dealing with currents or waves require specific practice. Try to get at least 4-6 open water sessions before race day. If truly impossible, race-day strategies like starting wide, sighting frequently, and remaining calm become even more critical.
What is a good finishing time for a first Half Ironman?
For first-time 70.3 athletes, finishing times typically range from 5-7 hours. A 6-hour finish is a solid goal for beginners with good fitness, while experienced athletes often target sub-5 hours. Elite athletes finish in under 4 hours. Focus on finishing strong rather than chasing a time goal in your first race.
How many brick workouts should I do per week?
Most athletes should complete 1-2 brick workouts per week during peak training. Early in your plan, one brick every 1-2 weeks is sufficient. Quality matters more than quantity—focus on teaching your legs to run off the bike with purpose. Even short 15-20 minute runs after bike workouts provide neuromuscular adaptation.
What should I eat during a Half Ironman race?
Aim for 200-300 calories per hour on the bike (gels, bars, sports drink) and 100-200 calories per hour on the run. Most athletes consume 1,200-1,800 total calories during a 70.3. The bike is your primary eating opportunity while the body is most stable. Practice your exact race nutrition strategy in training to avoid GI issues.
Should I do a full Ironman after my 70.3?
Many athletes use 70.3 as a stepping stone to full Ironman, but it's not required. The full Ironman demands significantly more training time (15-20+ hours/week) and a different mental approach. If you loved the 70.3 experience and have the time to commit, it's a natural progression. Otherwise, racing multiple 70.3s per season is a rewarding alternative.
Conclusion: Your 70.3 Journey Starts Now
The Half Ironman 70.3 is an extraordinary achievement that will test every aspect of your athletic ability. Unlike shorter races that reward raw speed, the 70.3 demands strategy, nutrition mastery, and the mental fortitude to keep moving when your body wants to quit.
Trust the process. Follow a structured plan, practice your nutrition, and approach race day with confidence in your preparation. The training is hard, but crossing that finish line—whether in 5 hours or 7—will be one of the most satisfying moments of your athletic life.
Welcome to the world of Half Ironman racing. See you at the start line.
Ready to Start Your 70.3 Journey?
Generate a custom training plan tailored to your schedule, fitness level, and race date.
Related Training Guides
Training for Your First Ironman
Ready for the full distance? Everything you need to know about Ironman preparation.
Open Water Swimming Guide
Master sighting, drafting, and race starts for triathlon success.
Nutrition for Endurance Athletes
Fuel your training and racing with science-backed nutrition strategies.
Recovery & Rest Day Strategies
Optimize recovery to absorb training load and prevent overtraining.