How do you prepare for a half marathon in 12 weeks?
You have signed up, the date is fixed and there are twelve weeks. What do you do in those weeks, and in what order, so that you stand on the start line with a long run in your legs and not with an injury?
Where you need to be when the twelve weeks begin
Twelve weeks is enough for a half marathon, on one condition: you already run. Three times a week, with a longest run of around eight to ten kilometres, is a starting point that twelve weeks can really work with. If you are starting from zero, the half marathon is a goal for a later calendar; the first months then go into the base, and that step cannot be skipped.
The reason lies in the difference between your heart and your legs. Your endurance grows in weeks; your tendons, bones and joint cartilage adapt over months. A schedule that takes you from five to twenty-one kilometres in twelve weeks asks your legs for something they can only deliver in six months. Hence the condition.
The long run grows from your own history
The heart of the preparation is one long, easy run per week. Not because it is hard, but because it is long: your body learns to use fat as fuel, your legs get used to the number of steps, and your head learns what the second hour feels like.
How long that run should be is not in a table but in your own log. Take your longest run of recent weeks as the starting point and make it one to two kilometres longer each week, with a week every three or four in which you deliberately shorten it. That way you arrive in week ten or eleven at around sixteen to eighteen kilometres. More is not needed: the last kilometres of the race you run on the tension of the day, not on a long run you have already done.
The long run is easy. Conversational pace, even when it feels slow. It is the most common mistake of these twelve weeks: running the long run at race pace, because race pace is, after all, the goal. Then it costs three days of recovery and the rest of the week is lost.
Easy as the base, hard as the exception
A split used widely in endurance sport is eighty-twenty: roughly four fifths of your running time easy, one fifth hard. Easy is the pace at which you talk in full sentences; hard is everything above it, from your threshold pace to short fast stretches.
In a week of three or four sessions that means: the long run easy, one or two short runs easy, and one session with hard work in it. That one session is enough. Two hard sessions in one week get in each other’s way, because you start the second before you have recovered from the first.
The hard work may change shape: one week blocks of a few minutes around your threshold pace, one week a longer stretch at goal pace, one week short, fast repetitions. The variety keeps it interesting and stimulates different sides of your fitness; its volume stays small.
A test at goal pace, halfway through
Around week seven or eight it is time for a benchmark: a session in which you run a good stretch, think eight to ten kilometres, at the pace you want to run on race day. Not to perform, but to measure. If the pace feels like something you could hold for another ten kilometres and more, your goal is realistic. If you are empty at the end, you know that now, and not at kilometre fifteen of the race.
Such a test gives you two things at once: an honest answer to whether your goal pace is right, and a reference the following weeks can be measured against. Be prepared to adjust your goal. A half marathon you finish at a slightly slower pace is a better experience than one you start at the planned pace and finish walking.
The taper: less volume, the same sharpness
In the last two weeks before the race you do less, not different. The volume goes down while the sessions keep their shape: still a bit of hard work, still a long run, but all of it shorter. Your body uses that room to shed the fatigue of ten weeks of build-up, while your fitness barely drops in those two weeks.
The trap of the taper is the rest itself. You feel fresh, you are nervous, and you want to do something more to be sure. That extra work no longer adds anything; everything you need on race day is in the weeks before. A taper belongs to distances from ten kilometres upwards. For shorter goals an easy final week is enough; a classic taper is then heavier than needed.
Eating and drinking on the way
A half marathon takes between one and a half and two and a half hours, and that is long enough to draw on your carbohydrate stores. A common guideline for efforts of that length is thirty to sixty grams of carbohydrate per hour: a gel or a few dates every half hour, or sports drink. What exactly you take matters less than having practised it.
You practise in the long run. Your stomach has to learn to eat while you run, and it only learns by doing it. From the long runs of twelve kilometres and up, take the same thing you want to use on race day, at the same moments. For the race itself: nothing new on the day.
You drink to thirst and to the weather. In cool weather a sip at the stations is enough; in heat you drink more and start earlier. Sweat loss varies a lot from person to person, so here too your own experience from the long runs is the better measure.
What Trimetra does with this
Put the race in the event calendar and the planner builds the weeks towards it: the long run grows from what you have already run, the hard work stays one session a week, and the last two weeks get shorter while the shape of the sessions stays. You get that taper for goals from ten kilometres upwards; for shorter goals it becomes an easy final week.
Your goal readiness sits in the app as a score from zero to a hundred, built from how regularly you train, how your recent load relates to your base and whether a benchmark on your goal distance has been run. Without that test, that part of the score stays empty; it does not invent a number.
If you have tapered before, the app looks at how you responded and shifts the volume of the next taper a little in that direction, within a narrow margin. What you eat on the way is shown with the session: thirty, sixty or ninety grams per hour, depending on duration and intensity. All of those numbers are proposals; you take them over or leave them.
Frequently asked questions
Can I run a half marathon without ever training 21 kilometres?
Yes, and that is the intention. A longest run of sixteen to eighteen kilometres is enough; the last kilometres come from the rest of the taper and the tension of the day. Running the full distance beforehand costs more recovery than it adds in certainty.
How often a week should I run for a half marathon?
Three to four times. One long easy run, one session with hard work and one or two short easy runs. More days only add something once you have kept those three or four up for months while staying fresh.
Should I eat during a half marathon?
With a running time of an hour and a half or more, it helps. Thirty to sixty grams of carbohydrate per hour is a common guideline. Practise it in your long runs, so your stomach already knows it on the day.
What if I am ill for a week during the build-up?
Carry on from where you were, not from where you wanted to be. One week costs little: you skip that week’s long run and the week after you pick up the last proven distance again. Catching up with two long runs in one week is exactly the spike that injuries come from.
Trimetra builds the weeks towards your race from your own history, sets the taper at the right distance and tells you per session what to eat on the way. If the build-up runs differently than planned, the goal moves along instead of the weeks.