The half marathon training plan that starts from what you run today

At 21.1 km, endurance takes over from speed. Half marathon prep comes down to three things: a long run that grows week after week, a fast session to hold your pace, and easy volume around them. You give your race date, the days you're available and what you run today: Trainetic works out the rest.

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The five rules of half marathon race prep

You'll find them in the reference plans, and your plan applies them.

Ten to twelve weeks for a first half. That's the length of the reference beginner programs: enough to grow the long run without skipping steps.

Start from a base. Beginner programs ask you to run about 5 km, three times a week, before you begin. If you're not there yet, the beginner plan gets you there in nine weeks.

The long run is the key session. It's what prepares your body to go the distance. It's run slowly — slower than race-day pace — and grows in stages.

Three sessions at least, four to be comfortable. Three are enough for a long run, a fast session and an easy run; the fourth adds easy volume.

Race-day pace comes at the end. In the final weeks, blocks at half marathon pace get your body used to the rhythm of the race.

What your plan lays out, based on your slots

You choose your days; the plan spreads the sessions across them, never placing two hard sessions less than two days apart.

Sessions per week	What the plan lays out	For a half
2	An easy run and a fast session	No long run: that's short for a half, and Trainetic tells you whether your slots are enough
3	A long run, a fast session, an easy run	The foundation of half marathon prep
4 or more	The same, plus easy volume — and, depending on your level, a second fast session	The most comfortable prep

One week in four, volume drops back to 75 %: that's the recovery week, when your body absorbs the previous three.

The sessions of half marathon prep

Each one has a clear role. None is there to fill the week.

The long run

It can go up to half of the week's volume, and stays capped at three hours. It's run at an easy pace: the goal is to last, not to go fast.

The fast session

Threshold and maximal aerobic speed (MAS) in the early and middle part of the plan, then blocks at half marathon pace — about 84 % of your MAS — as the race gets closer.

The easy run

Short and easy, it adds volume without adding fatigue. It also helps you recover from the previous day's session.

Are your slots enough?

A half marathon takes training time, and above all a slot long enough for the long run. When you create your plan, Trainetic compares the time you give it with the time half marathon prep requires at your level. If some is missing, it tells you, and suggests a longer prep or an extra slot.

The five most common mistakes

Running the long run too fast. Mistake No. 1. A long run at race pace leaves you tired for three days and prepares you no better. Slow, it builds; fast, it wears you down.

Going out too fast on race day. Over 21 km, every second gained in the first kilometer is paid back with interest by the fifteenth.

Betting everything on intervals. For a half, easy volume and the long run make the difference. One fast session a week is enough for most runners.

Skipping the recovery week. It isn't lost time: it's the week when the work of the previous three turns into fitness.

Trying something new on race day. New shoes, an unfamiliar gel, an unusual breakfast: the long run is where you test these things.

Where these numbers come from

Every benchmark on this page comes from a public source.

The twelve-week length and the starting base (about 5 km, three times a week) come from Hal Higdon's Novice 1 program, where the long run goes from 6 to 16 km.

Among recreational runners preparing for a half, the observed median is three sessions and 36 km a week (NURMI study, Frontiers in Physiology, 2021).

The reference training time by level comes from the 80/20 Endurance plans: it's what Trainetic compares your slots against.

The two-week taper, with reduced volume and maintained intensity, follows the meta-analysis by Bosquet (2007).

The questions runners ask before a half

What level do you need before preparing for a half?

Being able to run around thirty minutes without stopping, three times a week. If you're not there yet, start with the beginner plan, or with a 10 km plan.

How many weeks at minimum?

Ten to twelve for a first half. A runner who already runs regularly can prepare faster; your plan fits your race date and starts from your current volume.

Do you need to run 21 km in training?

No. Beginner programs cap the long run at around 16 km: race-day adrenaline and the taper do the rest. Running the full distance before the race tires you more than it reassures you.

How far should the long run be?

It grows in stages over the plan, up to half of your weekly volume at most. Your volume decides, not a fixed number.

Can you prepare for a half with three sessions a week?

Yes. It's actually the most common setup among recreational runners. A long run, a fast session, an easy run.

How do you set your target time?

From what you already run. A recent 5 or 10 km time gives your MAS, and your MAS gives a realistic projection over 21.1 km. If you're aiming much faster, Trainetic flags it before you train at a pace you can't hold.

Do you need a watch?

No. Your phone is enough: during the session, a voice announces each block, its duration and the target pace, and tells you when to slow down. If you already have a Garmin watch, the session is sent to it too.

Is it free?

Yes, for the essentials: creating your plan, taking it with you as a PDF, and running each session with voice guidance. A subscription is available for advanced features — automatic plan adjustments week after week, a written analysis of each session. The plan itself doesn't need it.