5K, 10K, half or marathon: which should I train for first?

Explainer 2 min read Updated 6 October 2026

Short answer

Pick the distance you can train for safely in the weeks you have. For most people starting out that is a 5K or 10K; a half or full marathon makes sense once you already run several times a week.

The longer the race, the longer the build-up and the bigger the weekly load.
A shorter race done well is a better first step than a long one done injured.
You can pick a longer race later and start that plan from your new level.

What changes with distance

The distance sets almost everything else in a plan: how long your longest run gets, how many weeks the build-up takes and how much running you do each week. A 5K plan tops out with long runs of around an hour. A marathon plan asks for long runs of two to three hours.

A simple way to choose

Not running yet, or only now and then: a 5K. It is a real goal, and it builds the habit everything else rests on.
Running most weeks already: a 10K or a half marathon.
Running regularly for months, and you have four or more months: a marathon is realistic.

When it is a specific race

If you have already entered a race, pick that distance. The plan then works out whether the date gives you enough time, and tells you if it looks tight.

In your plan

Your plan uses the distance to set your longest run and how fast your weekly running grows. If the date is close for the distance you picked, the plan builds more gently and tells you what is realistic.

Key points

What changes with distance

A simple way to choose

When it is a specific race

In your plan

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