How Long to Train for a 5K, 10K, Half Marathon or Marathon
Patricia Bedoya
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7
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Cover image generated with AI — © Chubby Studio S.L.
KEY TAKEAWAY
From a comfortable 5K base, a half marathon usually takes 12 to 14 weeks of training, and five to six months from no running at all. A 5K takes about nine weeks from zero, a 10K six to eight weeks more, and a marathon about 16 weeks on top of a solid base. Your tendons and bones, not your cardio, set the pace.
If you can already run about 5K comfortably, a half marathon plan usually takes 12 to 14 weeks. From no running at all, allow five to six months, because you need a 5K base first. As rough guides: about 9 weeks from zero to 5K, 6 to 8 more weeks for a 10K, and 16 weeks for a marathon.
Those numbers are where most plans land, and they are a fair starting point. But the calendar is not really set by your fitness. It is set by your legs, which adapt far more slowly than your heart and lungs. Here is what a sensible timeline looks like for each distance, how your starting point changes it, and how to tell from your watch that the weeks are working.
How long does it take to train for a 5K?
About nine weeks if you are starting from nothing. The NHS Couch to 5K programme runs for nine weeks at three sessions a week, with rest days in between, and finishes with 30 minutes of running without stopping. If you already run a little, four to six weeks of regular running is usually enough to finish a 5K comfortably.
Nine weeks is a template, not a deadline. Plenty of people repeat a week or two along the way, and a plan that takes twelve weeks has not failed. What matters in this phase is that the running happens three times a week, most weeks, and that it stays easy enough to hold a conversation.
How long does it take to train for a 10K?
Six to eight weeks if you can already run 5K without stopping, which is the common practice most 10K plans are built around rather than a figure from any study. From zero, stack the two: roughly nine weeks to reach 5K, then six to eight more, so about four months in total before a 10K feels comfortable.
The jump from 5K to 10K is mostly about time on your feet. A 10K is roughly an hour of running for many new runners, and the plan's job is to stretch your longest run toward that gradually. Speed can wait. If your first 10K is simply a steady run you finish feeling like you could have done a little more, the training worked.
How long does it take to train for a half marathon?
Twelve to fourteen weeks if you already run about 5K comfortably, a few times a week. St. Jude's plan for the Memphis half marathon, for example, runs 14 weeks and opens with two-mile easy runs and a three-mile long run. From no running at all, add the 5K and 10K stages first: five to six months is realistic.
This is the distance where the starting point matters most, because a half marathon asks for long runs of around 16 to 19 km, well beyond anything a beginner plan builds. A 12-week half marathon plan assumes the first few months of running are already behind you. If they are not, the honest move is to do those months first rather than squeeze them in.
Runners who have raced the distance before, or who already run 25 km or more a week, can often be ready in eight to ten weeks. That is not because the race got easier. It is because most of the adaptation it needs is already in place.
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How long does it take to train for a marathon?
Sixteen weeks is the standard, for runners who already have a solid base. The official London Marathon training hub offers four plans, from beginner to advanced, and every one of them is 16 weeks long. From no running at all, add the months it takes to build that base, and a first marathon becomes a project of about a year.
That base matters more than the plan's length. In a study of 662 marathon finishers, Rasmussen and colleagues found that runners averaging under 30 km a week before the race had about twice the injury risk of those running 30 to 60 km. It was a retrospective survey with self-reported injuries, so treat it as a strong hint rather than a rule. Still, it points the same way as common practice: arrive at the start of a marathon plan already running regularly, not planning to start there.
What actually limits how fast you can get race-ready?
Your tendons, bones and connective tissue, not your heart. Aerobic fitness responds within a few weeks of regular running, which is why the same pace starts to feel easier early on. Tendons and bone remodel much more slowly, so the week you feel ready for more is often weeks before your legs actually are.
A 2015 meta-analysis by Bohm, Mersmann and Arampatzis pooled 27 training studies on the Achilles and patellar tendons, each lasting at least eight weeks. Tendons did get stiffer and stronger with loading, and the effects tended to be larger in programs of twelve weeks or more, although that difference was not statistically significant. The broad message is that tendons adapt on a scale of months, and no plan can rush them.
That mismatch is why ramping up too fast is such a common mistake. Your breathing says yes, your Achilles has not voted yet, and how quickly your training load climbs decides which one you end up listening to.
Does the timeline change if you are coming back to running?
Yes, and usually in your favor, as long as you start from where you are now rather than where you were. Runners returning after a few months off tend to rebuild faster than true beginners, but the safe starting volume is your recent training, not your old personal best week.
If the break was an illness, expect your numbers to look worse than your fitness really is for a while, and read what your watch says after time off with that in mind. If the break was an injury, when and how much you can run again is a question for the physiotherapist or doctor treating it, and that answer sets your start date.
How can you tell from your watch that training is on track?
Look for three slow trends rather than any single run: a resting heart rate that drifts down across weeks, a cardio fitness estimate that creeps up, and familiar runs that cost less. If the same easy long run is showing a lower average heart rate at the same pace, your aerobic base is growing.
Each of these moves over weeks, not days, so check them weekly at most. A resting heart rate trend is noisy night to night and meaningful over a month. Apple Watch's cardio fitness estimate updates from outdoor walks and runs and is best read as a direction of travel, which is also why a low cardio fitness reading at the start of a plan is a starting line, not a verdict. The most honest signal is the simplest: your long run feels easier at the same heart rate than it did a month ago.
What happens if you squeeze a plan into fewer weeks?
The plan still has to cover the same ground, so every week gets steeper. Long runs grow faster, rest weeks disappear, and the jumps from one week to the next get bigger. Your legs pay for it, and a compressed plan is a classic setup for the kind of injury that ends the block altogether.
If the calendar is tight, there are better options than cramming. Pick a shorter race this season, or the same race next year. A half marathon you reach healthy beats a marathon you start injured, and the fitness you build in the meantime is not wasted: it is the base the longer plan was going to assume anyway.
FitWoody is an iOS app for iPhone, iPad and Apple Watch that turns your watch data into a clear read on how your body is doing. While you build toward a race, the useful parts are cardiac load, which scores each run by what it cost you internally, training load tracked against your own baseline, custom heart rate zones, and recovery baselines built from HRV, resting heart rate and sleep. Flyover replays your outdoor runs along the route. An Apple Watch is required, and it informs rather than diagnoses.
Give yourself the weeks the distance needs, and a few spare for the weeks life takes back. Showing up, in any form, counts.
Frequently asked questions
Is 8 weeks enough to train for a half marathon?
It can be if you already run regularly, around 25 km a week, or have raced the distance before. For someone who can only just run 5K, eight weeks is tight, and 12 to 14 weeks is the more common and safer range.
How long does it take to train for a marathon from scratch?
Roughly a year. Standard marathon plans, like the official London Marathon ones, last 16 weeks but assume you already run regularly. From no running at all, you first need a few months to reach 5K and then more months to build a steady weekly base.
Why can't you train for a race faster if you feel fit?
Because your heart and lungs adapt within weeks, while tendons and bones take months. Feeling fit only tells you about the fast half of that process. Squeezing a plan into fewer weeks makes the weekly jumps steeper, and the legs are what usually break.