The half marathon is 21.1 km, and for most first-timers it is the first race where endurance matters more than speed. It is a big step up from a 5K or 10K, but it is very achievable in 12 weeks if you start from the right place and build patiently. This guide sets out what you need before you start, how the 12 weeks fit together, what a training week looks like and how to fuel, taper and pace the day itself.
Before you start
Twelve weeks is a sensible first half marathon plan if you can already:
- Run 5K, or about 30 minutes, without stopping, at a comfortable pace.
- Run three times a week, and have done for at least a month or two.
- Find time for one longer run a week that will grow to two hours or so.
If you cannot run 30 minutes non-stop yet, start with our Couch to 5K plan and come back afterwards. Starting a half plan from scratch is the fastest route to injury. If you are already running 10K comfortably, you can follow the same shape with a little more distance, or run a shorter plan.
The 12-week shape
The plan moves through four phases. Base builds the habit and the easy mileage. Build adds one harder session a week and stretches the long run. Peak brings in some goal-pace running. Taper lets you recover so you arrive fresh.
| Week | Phase | Long run |
|---|---|---|
| 1 | Base | 8 km easy |
| 2 | Base | 9 km easy |
| 3 | Base | 10 km easy |
| 4 | Easier week | 8 km easy |
| 5 | Build | 11 km easy |
| 6 | Build | 12 km easy |
| 7 | Build | 14 km easy |
| 8 | Easier week | 10 km easy |
| 9 | Peak | 15 km, last 3 km at goal pace |
| 10 | Peak | 16 to 19 km easy |
| 11 | Taper | 12 km easy |
| 12 | Race week | Race day |
You do not need to run 21 km in training. A peak long run of 16 to 19 km, run slowly, is enough for a first half; race-day adrenaline and a taper carry you the rest. Newer runners should stop at about 16 km. Going further mostly adds tiredness and injury risk.
The easier weeks matter. Every third or fourth week, cut your distance back by about a fifth so your body can absorb the work. If a week goes badly, through illness or a busy patch, repeat it rather than skipping ahead.
A typical training week
On four days a week, a build-phase week might look like this:
- Tuesday: quality session. Threshold running, starting at about 15 minutes in one block and building towards 25 to 30 minutes, split into chunks like 3 x 8 minutes with a minute's jog. It should feel comfortably hard.
- Thursday: easy run. 5 to 8 km at a pace where you can chat.
- Saturday: easy run. Short and relaxed, 4 to 6 km. Skip it if you only run three days.
- Sunday: long run. From the table above, at easy pace.
Hard days never sit next to each other, and the long run follows an easy day. In the base weeks, Tuesday is just another easy run, perhaps with a few relaxed 20-second strides at the end.
Most of your running should be easy, roughly four runs in five. It is the long, easy miles that build the endurance a half needs. Our guide to easy running explains why holding back works, and the interval training guide covers threshold sessions in more detail.
Your paces
Your paces should come from a recent race, not a guess. Using Jack Daniels' VDOT system, a 25:00 5K runner would run easy at about 6:19 to 6:57 per km and threshold at about 5:16 per km, with an equivalent half marathon of 1:55:04. A 30:00 5K runner would run easy at about 7:30 to 8:13 per km, with an equivalent half of 2:18:10.
Treat those half marathon times as what proper training could make possible, not a promise. For a first half, finishing comfortably is a great goal in itself. The half marathon pace chart turns any finish time into kilometre splits, and the training paces page explains where the numbers come from.
Goal-pace work in the long run
From about week 9, try finishing every other long run with a few kilometres at your goal half marathon pace. Start with 2 to 3 km and, if you have a longer plan, build towards 5 km. The other long runs stay fully easy.
This does two jobs. It teaches you what race pace feels like on tired legs, and it shows you whether your goal is realistic. If 3 km at goal pace at the end of a long run feels very hard, your goal is probably too quick. Better to find out in week 9 than at mile 10.
Fuelling basics
On long runs under about an hour, you do not need anything but water if it is warm. Once your long runs pass about 90 minutes, start practising your race fuelling.
The long-standing guidance is 30 to 60 g of carbohydrate per hour during long events. Most gels contain about 20 to 30 g, so check the label. That works out at roughly one or two gels an hour, spread evenly. Practise with the exact gel or sweets you will use on race day, because some stomachs do not get on with certain brands.
Drink to thirst. Drinking far more than you need is not safer, and over-drinking can lead to hyponatraemia, which is dangerous. The long run guide covers fuelling in more depth.
The taper
Cut back for the last two weeks. A good half marathon taper drops your weekly distance to about 70% of your peak in week 11 and about half in race week, not counting the race. Keep a short session in each taper week, such as a few minutes at goal pace or threshold, so your legs stay sharp. Research on tapering supports cutting volume but keeping some intensity.
You may feel sluggish or restless during the taper. That is normal. Resist the urge to squeeze in one more long run; it is too late for it to help and early enough to leave you tired. The taper guide explains why.
Pacing the race
Most first half marathons go wrong in the first 5 km. You are fresh, the crowd is fast and goal pace feels easy, so you run quicker than planned. It costs you badly in the last third of the race.
- First 5 km: at goal pace or a little slower. Let people pass you.
- 5 to 16 km: settle into an even rhythm. Take your fuel as practised.
- Last 5 km: this is where the race really starts. If you have something left, speed up gradually.
Most distance world records have been run with even or slightly negative splits, and the same approach works for everyone else. Our race pacing guide has more on splits and race-day food, and a printable pace band keeps your splits on your wrist.
Build your plan
The half marathon training plan page shows how Run-R lays out the weeks. For a plan built around your own race date, recent time and the days you can run, with a two-week taper and goal-pace long runs in the peak weeks, use the plan builder. If you have a time in mind, try the sub-2 half marathon plan or the sub-2:30 plan.