A half marathon covers 21.0975 kilometres, or about 13.1 miles. It can be a rewarding next step once you have a consistent running base, but it asks for more sustained endurance, recovery planning and familiarity with longer outings than a 5K or 10K.

The right preparation is not simply to fit 21.1 kilometres into your calendar as quickly as possible. It is to arrive healthy, confident and able to manage the distance at a sensible effort. This guide offers a flexible 12-week example for runners who already run regularly and can complete approximately 6–8 kilometres comfortably. If that is not your starting point, build a base first and give yourself longer.

Start by checking your readiness

Before you begin, consider three questions:

  1. Can you run or run/walk consistently across several days each week?
  2. Does an outing of roughly 6–8 km feel manageable, without needing several days to recover?
  3. Can you make room for an occasional longer session and a lighter day afterward?

These questions do not determine who is allowed to attempt a half marathon. They help you decide whether a 12-week build is realistic for you. You can absolutely train for the goal using a longer timeline.

If you are still extending from five to ten kilometres, our first-10K guide offers a more appropriate first step.

What a balanced training week can look like

A simple structure for an established recreational runner might include one shorter easy run, one slightly longer midweek run, and a relaxed weekend long run. Depending on experience and recovery, a fourth easy day may or may not be appropriate.

Session Main purpose
Short easy run Maintain consistent low-stress movement
Midweek easy or controlled run Practise steady effort and routine
Weekend long run Build comfort with longer time on your feet
Recovery days Rest, walking or gentle activity as appropriate

There is no reason for every session to be long. Keep most outings comfortable enough that you can speak in sentences. Rest days help the training fit together.

A flexible 12-week long-run example

The distances below describe the longest outing of the week only, not total weekly distance. They are an example for someone with an existing base, not a universal prescription. Easy effort, recovery and individual circumstances should determine whether you repeat, reduce or extend a week.

Week Example longest outing Notes
1 8 km Establish comfortable rhythm
2 9 km Add a little time moving
3 10 km Assess recovery
4 8 km Lighter consolidation week
5 11 km Practise route and hydration planning
6 12 km Maintain easy intensity
7 14 km Check shoes and fueling tolerance
8 10 km Lighter week
9 15 km Practise event-morning routine
10 16–18 km Longest outing only if appropriate
11 12 km Reduce load; focus on recovery
12 Half marathon Start conservatively, adapt as needed

There is no requirement to run the full half-marathon distance in training. Some runners prefer a shorter longest outing, particularly when a longer distance would mean spending an excessive time on their feet. Others need additional weeks to reach the same readiness.

Keep long runs easier than race effort

Long runs are generally a chance to practise moving comfortably for a longer period. A pace that feels fine for 5 km may become too demanding after 15 km. Start slowly and use walking breaks when helpful.

Plan a route with suitable water access and an option to shorten it if necessary. Check the weather. A hot day may call for a reduced distance or earlier start.

Think about the duration of your outing as well as the kilometres covered. For a slower runner, the same distance can mean substantially more time moving. More is not automatically better if recovery starts to suffer.

Practise drinking and fueling before race day

As sessions get longer, your nutrition needs may change. Sports nutrition guidance commonly discusses carbohydrate during sustained exercise of roughly 1–2.5 hours, often around 30–60 grams per hour depending on intensity and tolerance. That is a broad reference range, not a target everybody must consume. https://www.usada.org/wp-content/uploads/2026-TS-Nutrition-Guide.pdf

Experiment during selected training sessions rather than on event day. Identify foods or products your stomach tolerates. Drink according to conditions, thirst and your own needs; avoid forcing large amounts of water.

For more practical race planning, see Half Marathon Pacing and Fueling.

How to set a reasonable finish goal

If this is your first half marathon, completing it at a controlled effort is a legitimate goal. A prior race result can help establish a possible pace, but a mathematical prediction does not show whether you have built the endurance necessary for 21.1 km.

A 2-hour half marathon is approximately 5:41 min/km. A 2-hour-15-minute finish is approximately 6:24 min/km. These are arithmetic examples, not recommended speeds for beginners.

Use the Running Pace Calculator or Split Calculator to explore a plan, and then judge whether that goal fits recent long-run experience and weather conditions.

The final week should feel lighter

You cannot create an entirely new endurance base in the final few days. Focus instead on arriving rested, keeping a familiar routine, checking your kit and learning how the start area works.

Reduce the burden of training rather than squeezing in one final big session. Practise the breakfast and hydration routine you know agrees with you; avoid introducing new shoes or energy products at the last moment.

Common half-marathon preparation mistakes

Pushing long runs too fast. The long outing does not need to feel like a race.

Adding mileage and speed simultaneously. A jump in several training stresses may be hard to recover from.

Ignoring rest. Regularly poor sleep or persistent soreness deserves attention.

Copying a plan that starts above your ability. You can lengthen the build rather than force a schedule.

Trying unfamiliar fueling on race day. Practise during training where possible.

Frequently asked questions

Do I have to run 21 km before my first half marathon?

No. Many plans use a shorter longest run. The ideal amount depends on your background, pace, recovery and support.

Is twelve weeks enough to prepare?

For someone with a suitable running base, it may be. Someone starting from very little running often needs more time.

Can I use run/walk intervals in a half marathon?

Yes, if permitted by the event. A planned pattern may help you manage effort, especially over longer durations.

How fast should my long runs be?

Often comfortably slower than planned race effort. Aim for a repeatable pace that allows reasonable recovery afterward.

Should I take a gel on every long run?

Not necessarily. Fueling needs vary with duration and intensity. Practise options appropriate to your session and consult a qualified professional if you need individualized nutrition advice.

Build confidence through preparation

A successful first half marathon is often the result of ordinary training weeks done consistently. Keep easy days easy, learn from longer outings, and adapt the schedule rather than forcing it.

When you are ready to plan the event itself, read our Half Marathon Pacing and Fueling Guide and make your target split table with the Split Calculator.