Half Marathon Training Plan: A Complete Guide to Your First 13.1 Miles

You can run a half marathon. That is not motivational fluff. If you can currently run three miles without stopping, a structured 12-week training plan will carry you to 13.1. The distance is challenging, but the path to get there is straightforward: build mileage gradually, run most of your miles at an easy pace, and give your body enough recovery time to absorb the work.

Our platform SensAI uses wearable data from your Apple Watch, Garmin, or Oura ring to adapt your training based on actual recovery status rather than a fixed calendar. But whether you train with AI guidance or a printed schedule on your fridge, the principles in this guide apply. Here is everything you need to prepare for your first half marathon, including a complete 12-week training plan you can start today.

The Half Marathon Distance

A half marathon covers 13.1 miles (21.1 kilometers). It is the most popular race distance in the United States, with approximately 2 million finishers annually, four times the number who complete full marathons.¹ The distance sits in a productive middle ground: long enough to demand real preparation, short enough that training does not consume your entire schedule. Many runners treat it as a stepping stone toward a full marathon, but it is also a worthy goal on its own.

Timeline for Half Marathon Training

The answer depends on your current fitness. Former Olympic marathoner Mark Coogan puts it simply: “If you can run a 5K now, then you can run a half marathon in eight weeks.” He adds that the ideal plan is three to four months, which provides buffer for illness, injury, or a busy week at work.²

Hal Higdon’s popular Novice 1 program assumes you can run three miles and builds to race readiness over 12 weeks. Most plans fall in the 10 to 16 week range.

Starting Fitness Level	Recommended Plan Length	Prerequisite
Can run 3 miles	12-16 weeks	Comfortable running 3x/week
Can run a 5K	10-14 weeks	Running 3x/week consistently
Can run a 10K	8-12 weeks	Running 4x/week, 15+ miles/week
Experienced runner	6-10 weeks	Running 20+ miles/week base

If you are not yet able to run three miles continuously, build to that baseline first. Jumping into a half marathon plan too early is the fastest route to shin splints and frustration.

Essential Components of a Half Marathon Training Plan

Every effective half marathon plan combines five types of training. The specific days and distances vary between programs, but these building blocks remain constant.

Long Runs

The long run is the single most important workout in your training week. It builds the aerobic endurance and mental toughness you need to cover 13.1 miles on race day. Your long run should increase gradually each week, starting around 4 miles and peaking at 10 to 12 miles.

You do not need to run the full 13.1 before race day. As Coogan notes, “If you can run 10 miles, you can run 13 on race day.” The combination of taper rest and race day adrenaline bridges that gap. Run your long runs at a conversational pace where you could speak in full sentences. If you are gasping between words, slow down.

Easy Runs

Easy runs should make up roughly 80% of your weekly mileage. These runs build your aerobic base, the engine that powers everything else, without taxing your recovery. Keep your heart rate in Zone 2 (65 to 80 percent of your maximum), which translates to a pace where you can hold a conversation comfortably.

The most common mistake runners make is turning easy days into moderate efforts. If your easy runs feel too easy, you are doing them right.

Speed Work

Speed sessions improve your running economy and prepare you to hold a faster pace on race day. Plan for one to two speed workouts per week. The main types include:

Intervals: Repeated fast efforts with recovery (such as 4 to 6 x 400m at 5K pace with a 90-second jog between each)
Tempo runs: Sustained efforts at a pace slightly faster than your half marathon goal pace, typically 15 to 20 minutes
Fartlek: Unstructured alternating between fast and easy running during a continuous run
Strides: Short 20 to 30 second accelerations at the end of an easy run to build leg speed

The Boston Athletic Association’s half marathon plans use “half marathon simulations” where runners practice goal pace within longer runs, an effective way to rehearse race conditions.³

Cross-Training and Strength Work

Running alone is not enough. Most coaches recommend two strength training sessions per week, prioritizing lower body and core exercises like squats and deadlifts alongside split squats and lunges.⁴ Strength work prevents the overuse injuries that sideline runners mid-plan.

Cross-training days like swimming or cycling let you build cardiovascular fitness without the impact stress of additional running miles. Use these days to stay active while giving your joints a break.

Rest and Recovery

Rest days are not wasted days. Your body adapts and grows stronger during recovery, not during the run itself. Schedule at least one full rest day per week, and always take an easy or rest day after your long run.

If you track heart rate variability as a recovery signal, a downward HRV trend across several days indicates your body has not fully absorbed recent training stress. That signal means it is time to pull back, not push through.

Component	Frequency	Intensity	Purpose
Long Run	1x/week	Easy (conversational)	Build endurance
Easy Runs	2-3x/week	Zone 2 (65-80% max HR)	Aerobic base
Speed Work	1-2x/week	Zone 3-4	Improve pace and economy
Strength	2x/week	Moderate	Injury prevention and power
Rest	1-2x/week	None	Recovery and adaptation

12-Week Half Marathon Training Plan

This plan is designed for beginner to intermediate runners who can currently run 3 to 4 miles comfortably. It follows a four-run-per-week structure with cross-training and strength sessions plus dedicated rest days built in. Long runs build from 4 miles to a peak of 10 miles before a two-week taper.

How to read this plan:

Easy = conversational pace, Zone 2 heart rate
Long = same easy pace, just farther
Speed = intervals, tempo, or fartlek (varies by week)
XT = cross-training (cycling, swimming, or walking)
Strength = lower body and core focus, 30-40 minutes

Week	Mon	Tue	Wed	Thu	Fri	Sat	Sun	Total
1	Rest	3 mi easy	XT	3 mi easy	Strength	4 mi long	Rest	~10 mi
2	Rest	3 mi easy	XT	3 mi easy	Strength	4.5 mi long	Rest	~10.5 mi
3	Rest	3.5 mi easy	Speed: 3 mi with 4x400m	3 mi easy	Strength	5 mi long	Rest	~14.5 mi
4	Rest	3 mi easy	XT	3 mi easy	Strength	4 mi long	Rest	~10 mi
5	Rest	4 mi easy	Speed: 4 mi tempo (2 mi at HM pace)	3 mi easy	Strength	6 mi long	Rest	~17 mi
6	Rest	4 mi easy	Speed: 4 mi with 5x400m	3 mi easy	Strength	7 mi long	Rest	~18 mi
7	Rest	4 mi easy	Speed: 4 mi fartlek	3.5 mi easy	Strength	8 mi long	Rest	~19.5 mi
8	Rest	3 mi easy	XT	3 mi easy	Strength	5 mi long	Rest	~11 mi
9	Rest	4.5 mi easy	Speed: 5 mi tempo (3 mi at HM pace)	3.5 mi easy	Strength	9 mi long	Rest	~22 mi
10	Rest	4.5 mi easy	Speed: 5 mi with 4x800m	3.5 mi easy	Strength	10 mi long	Rest	~23 mi
11	Rest	4 mi easy	Speed: 4 mi with 3x800m	3 mi easy	Strength	6 mi long	Rest	~17 mi
12	Rest	3 mi easy	2 mi easy	Strength	Rest	Rest	Race: 13.1 mi	~18 mi

Notes on this plan:

Week 4 and Week 8 are intentional step-back weeks where mileage drops. These recovery weeks let your body consolidate the fitness gains from the previous building phase.
Your training frequency and rest scheduling can shift to fit your schedule. If Thursday works better for your long run than Saturday, move it. Consistency matters more than which specific day you run.
Speed work intensity should feel challenging but controlled. You should finish speed sessions tired, not destroyed.

Race Day Nutrition and Hydration

Your fueling strategy needs to be tested and refined during training, not invented on race morning. The core principle: practice everything you plan to do on race day during your long runs first.

Pre-race fueling timeline:

Timing	What to Do
Night before	Carb-rich dinner you have eaten before (pasta or rice with lean protein). Nothing new.
2-3 hours before	Light breakfast: toast with peanut butter, oatmeal, or a bagel. 16-20 oz water.
30 min before	6-8 oz water or sports drink. Optional: half an energy gel.
During race	30-60 grams of carbs per hour from gels, chews, or sports drink.
Every 15-20 min	3-6 oz water or electrolyte drink at aid stations.⁵

Even 2% dehydration can measurably slow your performance. On runs longer than 60 minutes, carry water or plan a route with access to hydration. Experiment with different gels and sports drinks during training to find what your stomach tolerates.

Common Half Marathon Training Mistakes

Running too fast on easy days. If you cannot hold a conversation, you are running too hard. Easy runs should feel genuinely easy. Pushing the pace on recovery days accumulates fatigue that undermines your harder sessions.
Skipping rest days. More running does not always equal faster improvement. Your muscles and connective tissue need unloaded time to repair and adapt. Replacing rest days with extra runs increases your risk of overuse injuries.
Increasing mileage too quickly. The general guideline is to add no more than 10% to your weekly mileage. Jumping from 15 to 25 miles in a single week invites problems that can derail your entire plan.
Ignoring early warning signs. A persistent ache in one spot is different from general muscle soreness. Catching a minor issue early might cost you one or two days off. Ignoring it could cost you the entire race. Knowing when fatigue crosses into overtraining is a skill worth developing.
Testing new gear or nutrition on race day. Race morning is not the time to break in new shoes, try an unfamiliar energy gel, or eat a breakfast you have never tested. If you have not worn it or eaten it during a long run, leave it at home.
Skipping the taper. Most runners should taper for about two weeks before a half marathon, with the last hard workout roughly 10 days out.⁶ Cutting volume feels counterintuitive, but the accumulated rest is what makes you feel sharp on race day.

How Wearable Data Personalizes Your Half Marathon Training

Every training plan printed in a book or posted online assumes your body will be equally ready to train on the days it prescribes. That assumption rarely holds. A poor night of sleep, a stressful week at work, or a low-grade cold all shift your actual readiness in ways a static schedule cannot account for.

Wearable devices track the biometric signals that reflect this readiness in near real time. Heart rate variability measures the balance of your autonomic nervous system: consistent or rising HRV values indicate recovery, while a declining trend over multiple days signals accumulated fatigue. Resting heart rate rising above your personal baseline confirms the pattern. Sleep quality metrics add further context by revealing whether you are actually getting the deep, restorative sleep your body needs between training sessions.

A static plan gives you a fixed weekly schedule and ignores daily readiness variation. Adjusting by feel is better, but subjective self-assessment is prone to bias. A wearable-informed plan sits at the other end of the spectrum: AI analyzes your HRV, sleep, and training load to adjust your workouts daily. The tradeoff is that you need to wear your device consistently.

The practical difference: on a day when your HRV has been declining and your sleep was fragmented, a static plan still demands your scheduled tempo run. A wearable-informed approach recognizes the fatigue pattern and swaps to an easy run or rest day. When your metrics recover, intensity scales back up. Translating wearable data into actionable training decisions turns a one-size-fits-all plan into something that adapts to your life.

SensAI’s Approach to Half Marathon Training

We built SensAI to put these adaptive training principles into practice. The app connects to your Apple Watch or Garmin alongside Oura ring and Fitbit, then reads your HRV, sleep quality, resting heart rate, and accumulated training load daily.

Rather than locking you into a fixed 12-week schedule, our AI adjusts your running plan based on what your body can actually handle today. It maintains context across weeks and months of your personal data, tracking your mileage progression and flagging when you need to pull back or when you are ready to push harder. The result is a half marathon training plan that flexes around your recovery, your schedule, and your life.

Download SensAI on the App Store to let your biometric data guide your half marathon training.

FAQs About Half Marathon Training

How many days a week should I run when training for a half marathon?

Most beginner plans call for three to four running days per week. More experienced runners may run four to five days. The remaining days should include cross-training, strength work, and at least one full rest day.

Do I need to run 13.1 miles before race day?

No. The standard peak long run is 10 to 12 miles. Race day adrenaline plus the fitness you built during taper carry you the remaining distance. No major training plan requires a full 13.1-mile run before the race.

Can I walk during a half marathon?

Yes. The run/walk method is a legitimate and effective strategy. Many runners alternate between running and walking intervals throughout the entire race. Jeff Galloway, a former Olympian, was a well-known advocate of this approach.

What pace should I run my training runs?

The majority of your training runs should be at conversational pace, slow enough that you could talk to a running partner in full sentences. Only your speed work sessions (one to two per week) should feel genuinely hard.

What should I eat the night before a half marathon?

A carb-rich dinner that you have eaten before and know your stomach handles well. Pasta, rice with lean protein, or a similar meal works for most runners. Avoid high-fiber, high-fat, or unfamiliar foods that could cause digestive issues on race morning.

How do I know if I’m overtraining?

Warning signs include persistent fatigue despite adequate sleep, declining performance on runs that previously felt manageable, elevated resting heart rate, nagging joint or muscle pain, and loss of motivation. If you track biometric data, a sustained downward trend in HRV is one of the earliest and most reliable signals.

References

Higdon H. “Novice 1 Half Marathon Training Program.” halhigdon.com, 2025. https://www.halhigdon.com/training-programs/half-marathon-training/novice-1-half-marathon/ ↩
Carter K. “Half Marathon Training for Beginners.” Runner’s World, 2025. https://www.runnersworld.com/training/a20843627/half-marathon-training-for-beginners/ ↩
Boston Athletic Association. “Training Plans - Boston Half.” baa.org, 2025. https://www.baa.org/races/boston-half/info-for-athletes/boston-half-training/ ↩
Sayer A. “Strength Training For Runners.” Marathon Handbook, 2025. https://marathonhandbook.com/strength-training-for-runners/ ↩
Merkel J. “Hydration for a Half Marathon.” Nutrition for Running, 2023. https://nutritionforrunning.com/hydration-for-a-half-marathon/ ↩
“How to Taper for a Half Marathon: Step-by-Step Guide.” OC Marathon, 2024. https://ocmarathon.com/how-to-taper-for-a-half-marathon/ ↩