12-week half marathon training plan (for runners who can run 5K)
A complete 12-week half marathon training plan for runners who can already run 5K. Week-by-week table, VDOT pacing, long-run fueling, taper, and race-day pacing.
17 June 2026
You can run 5K, and now 21.1 kilometres has your attention. The half marathon is the perfect next distance: long enough to demand real training, short enough that you do not have to rebuild your life around it. Twelve weeks is the right amount of time to get there properly from a 5K base, building your long run from a comfortable 8 km all the way up to 18 or 19 km, so that on race day the full distance feels like the natural extension of everything you have already done. This is a complete half marathon training plan, written out week by week, with the pacing, the fueling, and the race-day strategy that turn a finish into a finish in control.
Nothing here is gated. The full 12-week plan, every week and every run, is below. If you never sign up for anything, you still have a complete plan you can follow start to finish.
The honest prerequisite: run 5K continuously first
This is not a couch to half marathon plan, and being clear about that protects you from injury. Before week 1, you should be able to run 5 kilometres continuously, even slowly, without dropping to a walk. That is the real entry requirement. Every week of this plan builds on top of an existing aerobic base rather than creating one from scratch, and the long-run progression assumes your legs and connective tissue already tolerate half an hour of continuous running.
If you cannot yet run 5K without walking breaks, you are not behind, you are simply at an earlier stage. Spend four to six weeks building a continuous 5K first with a run-walk approach, shrinking the walk intervals until you can run the whole thing. If you can run 5K but have never raced longer, building to a 10K first is an excellent on-ramp, and our 8-week 10K training plan takes you there with the same easy-and-quality structure you will use here. Trying to skip straight to half marathon volume off a shaky base is the single most common reason new runners pick up a calf or shin injury in week 5 and never make the start line.
You do not need to be fast and you do not need racing experience. You need that continuous 5K, four runs a week, and the patience to let the long run grow gradually.
How the plan is structured
The plan runs four sessions a week, organised around a simple, durable idea: one long run and one quality session per week, with the rest of your running kept genuinely easy. Each run has a specific job:
- Two easy runs. The backbone of every week. Run at conversational pace, slow enough to hold a full conversation. These build the aerobic engine that carries you through 21 km, and they make up most of your weekly volume.
- One quality session. A single harder effort each week, a tempo run, a threshold workout, or some race-pace running. This is where your half-marathon-specific fitness is built: the ability to hold a strong, sustainable pace for over an hour.
- One long run. The most important session of the week and the one that defines half marathon training. It steadily extends the distance you can cover, builds the durability the back half of the race demands, and rehearses your fueling and pacing.
The twelve weeks move through four phases. Base (weeks 1 to 4) establishes the routine and lifts your long run toward 10 km. Build (weeks 5 to 8) adds volume and introduces threshold work. Peak (weeks 9 to 11) takes the long run to its 18 to 19 km maximum and sharpens race-pace fitness. Taper (week 12) drops the volume sharply so you arrive at the start line fresh. The long run grows by roughly ten percent a week, with deliberate cutback weeks every fourth week so the training sticks instead of grinding you down.
The 12-week half marathon plan week by week
Distances are in kilometres and include warmup and cooldown jogging inside the quality sessions. Take at least one full rest day every week, and never schedule your quality session and long run on back-to-back days. If a number feels too ambitious in a given week, repeat the previous week rather than forcing it: consistency across twelve weeks beats two heroic weeks followed by a strained tendon.
| Week | Quality session | Easy run | Easy run | Long run | Weekly total |
|---|---|---|---|---|---|
| 1 (base) | 5 km (incl. 3 km tempo) | 4 km | 4 km | 8 km | ~21 km |
| 2 (base) | 6 km (incl. 4 km tempo) | 5 km | 4 km | 9 km | ~24 km |
| 3 (base) | 6 km (incl. 5 × 3 min @ threshold) | 5 km | 5 km | 10 km | ~26 km |
| 4 (recovery) | 5 km easy + strides | 4 km | 3 km | 7 km | ~19 km |
| 5 (build) | 7 km (incl. 5 km tempo) | 5 km | 5 km | 12 km | ~29 km |
| 6 (build) | 8 km (incl. 2 × 3 km tempo) | 6 km | 5 km | 13 km | ~32 km |
| 7 (build) | 8 km (incl. 6 × 3 min @ 10K pace) | 6 km | 6 km | 15 km | ~35 km |
| 8 (recovery) | 5 km easy + strides | 5 km | 4 km | 11 km | ~25 km |
| 9 (peak) | 9 km (incl. 6 km @ half-marathon pace) | 6 km | 6 km | 16 km | ~37 km |
| 10 (peak) | 9 km (incl. 3 × 3 km @ HM pace) | 6 km | 6 km | 18 km | ~39 km |
| 11 (peak) | 8 km (incl. 5 km @ HM pace) | 6 km | 5 km | 19 km | ~38 km |
| 12 (taper / race) | 5 km easy + strides | 4 km | rest | half marathon | ~13 km + race |
Notice weeks 4 and 8 are deliberate cutbacks. Your fitness is built during recovery, not during the hard weeks, and dropping the volume every fourth week is what lets the next block of training stick instead of accumulating into an injury. Do not skip them because you feel strong. Feeling strong in a recovery week is the whole point: it means the previous block worked.
This is also the right moment to set a realistic goal time, because training toward a number sharpens every session. The Run Coach takes your current run pace and turns it into a projected finish time that updates every time you log a faster effort, so you can watch whether your tempo and race-pace work is actually moving the number. Personalize this plan to your own pace and you will know, well before race week, exactly what half marathon time you are on track for.
Pacing: set your paces from a real race, not a feeling
The single biggest mistake new distance runners make is running their easy runs too fast and their quality sessions not hard enough, so every run collapses into the same mediocre middle pace. Your easy runs should be genuinely easy, slow enough to hold a full conversation in complete sentences without gasping. It will feel almost embarrassingly slow at first, and that is correct. This is where the large majority of your aerobic engine gets built, and protecting the easy pace is what makes your hard days productive.
Your quality sessions are the opposite. Tempo running sits at a "comfortably hard" effort you could hold for about an hour, breathing hard but in control. Threshold intervals are a touch faster with short recoveries. And from week 9 onward, the half-marathon-pace segments rehearse exactly the speed you intend to race at, so race day feels familiar rather than new.
The clean way to set all of these is from a recent race or time trial, converted into precise training paces, rather than guessing. A single hard 5K tells you your easy pace, your tempo pace, your threshold pace, and your goal half marathon pace. The method is covered in full in VDOT training paces explained, which walks through how one race result via Jack Daniels' VDOT system unlocks every training pace you need. Or skip the tables entirely and plug your time into the free running pace calculator to read off each pace in seconds.
Fueling the longer long runs
Up to about 75 to 90 minutes of running, your body's stored glycogen covers the effort and you do not need to eat mid-run, just run well hydrated. Beyond that, and your long runs from week 7 onward will cross it, you start running low on fuel, and the back half of a long run becomes a grind that has nothing to do with your fitness. This is where in-run fueling matters, and the long runs are exactly where you rehearse it so race day holds no surprises.
The practical rule for the half marathon distance: on any long run over about 90 minutes, take in 30 to 60 grams of carbohydrate per hour, starting around the 45-minute mark before you feel you need it. That is roughly one gel every 35 to 45 minutes, or the equivalent in chews or sports drink. Sip water regularly rather than gulping at the end, and in hot weather lean toward a drink with electrolytes. The golden rule is nothing new on race day: whatever gel, chew, or drink you plan to use in the race must be tested on your long runs first, because every gut tolerates different products differently and the long run is where you find out which ones sit well. By week 10 and 11 you should have a fueling routine you trust completely.
Race-day pacing: even, or a slight negative split
You have done twelve weeks of work. Race day is about not wasting it, and the way runners waste it is by going out too fast. Adrenaline, a crowd, and a two-week-fresh taper conspire to make your first few kilometres feel effortless at a pace you cannot possibly hold for 21. Almost every first-timer makes this exact error and pays for it brutally somewhere after kilometre 15.
The goal is an even pace, or a slight negative split, where your second half is as fast as or marginally faster than your first. Practically, that means holding yourself back early. For the first 3 to 4 km you should feel like you are running slightly too slow, deliberately leaving fuel in the tank. Lock into your goal pace by kilometre 5, hold it steady through 15, and only if you genuinely feel strong do you start pressing from kilometre 16 onward. The runner who negative-splits reels in a stream of people who blew up in the closing kilometres. The runner who banks time early becomes one of those people.
A simple check: if your first kilometre feels comfortable and controlled, you have it right. If it feels good and fast, you are going too hard. Trust the even-pace plan over how good your legs feel in the opening minutes, and trust the race-pace long runs you already rehearsed.
Common first half marathon mistakes
- Skipping the 5K prerequisite. Jumping into half marathon volume without a continuous 5K base is the fastest route to a shin or calf injury. Build the base first.
- Running every run at the same pace. Easy days too fast, quality days too soft. Keep easy genuinely easy and the quality session genuinely hard, and the plan works as designed.
- Chasing long-run distance too fast. The roughly ten-percent weekly progression exists for a reason. Adding a big jump because you feel keen is how niggles become injuries.
- Skipping recovery weeks and the taper. Weeks 4, 8, and 12 are part of the training, not optional rest you have earned. Skipping them leaves you flat or hurt on race day.
- Not practising fueling. A first gel taken during the race itself is a gamble. Rehearse fueling on every long run over 90 minutes.
- Going out too fast. The most expensive mistake. A fast first 5 km followed by a death march is always slower than an even effort.
Turn the plan into a target time
This plan gets you to the start line ready to finish your first half marathon in control. If you want to know what time you are actually on track for, and which sessions are moving the needle, the Run Coach turns your run paces into a projected finish time that updates every time you log a faster effort, so the goal stops being a guess. Its run-projection engine was built for the run-plus-strength demands of Hyrox, but it works just as well for a standalone half, and the AI coach reviews your logged sessions and tells you what to adjust each week. When 21.1 km starts to feel routine and a longer goal calls, the 16-week marathon training plan is the natural next step.
Frequently asked questions
Can I train for a half marathon in 12 weeks?
Yes, if you can already run 5K continuously before you start. Twelve weeks is enough to safely build your long run from around 8 km up to 18 or 19 km, develop the tempo and race-pace fitness the distance demands, and taper into the race fresh. If you cannot yet run 5K without walking, build that base first, or step up through a 10K before committing to a half.
How long should my longest run be before a half marathon?
For a first half marathon, peaking at 18 to 19 km about two weeks out is ideal. You do not need to run the full 21.1 km in training: race-day adrenaline, the taper, and the crowd reliably carry you the final couple of kilometres. Running the full distance in training mostly adds fatigue and injury risk without adding fitness, which is why this plan caps the long run just below race distance.
How many days a week should I run?
Four sessions a week is the target: two easy runs, one quality session, and one long run. Take at least one full rest day and avoid scheduling the quality session and long run on consecutive days. If four runs is too much for your schedule or recovery, drop one easy run to three sessions, but protect the quality session and the long run, since they do the most work.
What pace should I run my long runs at?
Mostly easy, conversational pace, the same effort as your easy runs. The long run's job is time on feet and durability, not speed, so resist the urge to push it. The exception is the peak-phase long runs from week 9, where you fold in segments at goal half-marathon pace to rehearse race effort on tired legs. Set both your easy and race paces precisely from a recent 5K using the running pace calculator rather than guessing.
How should I fuel during the race?
For most runners a half marathon takes between about 90 minutes and a little over two hours, which crosses the threshold where in-run fuel helps. Aim for 30 to 60 grams of carbohydrate per hour, roughly a gel every 35 to 45 minutes, starting before you feel you need it, and sip water regularly. Critically, use only what you have already tested on your long runs. Nothing new on race day.
To turn this plan into a projected finish time and track whether your training is working, open the Run Coach. To dial in your exact training paces from a recent 5K, read VDOT training paces explained or use the running pace calculator, and when you are ready to step up, the 16-week marathon training plan takes you to the full distance.