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Race training

Run a strong
half marathon.

The half marathon is the first distance where the long run runs the show. It is long enough to punish a shallow aerobic base and short enough to reward a well-paced threshold effort. Get the long run and the base right, and 21.1 km is finished strong, not survived.

01 / The demands

What the half marathon actually demands

The half marathon sits in an unusual middle ground. It is long enough that a shallow aerobic base gets exposed in the final 5K, the same way it would in a marathon, but short enough that race pace still sits close to your lactate threshold, the way it does in a 10K. It asks for both qualities at once, and most training plans get the balance wrong.

This is why the half punishes shortcuts in either direction. Train only long and slow and you show up under-sharpened, unable to hold a real pace. Train only for speed and the long run never gets the volume it needs, so you fade with 5 km left no matter how fast your legs feel early. The distance rewards a deep base with a sharpened edge on top, built in that order.

Short answer

To train for a half marathon, run four to five days a week for 10 to 14 weeks: a long run that builds patiently to 18 to 20 km, one threshold session, and two to three easy runs, all shaped around roughly 80 percent easy volume. Race pace is your goal time divided by 21.1, and the reliable way to a strong finish is even pacing off a deep base, not a fast start.

The key number

80%

of your weekly volume should stay easy, even during a half marathon block. The one hard session sharpens race pace. The easy 80 percent, led by the long run, is what lets you actually hold it for 21.1 km. Reverse the ratio and the long run stops building you and starts breaking you down.

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Interactive calculator

Your half marathon
pace ladder.

Set your goal half marathon time. Your race pace updates in real time, along with the training paces that build it. Estimates, not gospel, a starting point for structuring the week.

Goal half marathon time

1:45:00

Your half marathon race pace

4:59

per kilometre

Race pace is your goal time divided by 21.0975 km. Training paces are estimates derived from that race pace using established pace relationships. They are a starting point for structuring a week, not a substitute for testing your own threshold and zones.

03 / Systems

Why most half marathon runners fade at 16 km

Almost never a fitness problem on race day itself. It is a base problem, decided weeks earlier. When the long run gets skipped or shortened for convenience, or run too fast because it feels good early, the aerobic durability that should carry you through the last 5 km never gets built. The engine feels fine at 10 km and empty at 16.

The fix is not more running. It is more of the right running: a long run that grows steadily, run genuinely easy, so it builds you instead of breaking you down. Speed does not fix a base problem. Only time spent at an easy, sustainable effort does.

The systems a half marathon is built on

Three trainable qualities decide your half marathon time. Develop them in the right order and race day mostly takes care of itself.

1. Aerobic base

The base is the size of your engine, and for the half it is the single biggest lever available. Built almost entirely with easy, conversational running in Zone 2, it determines how much of the race you can run aerobically before real fatigue sets in. A deeper base pushes your threshold higher and makes race pace feel more sustainable, not just faster in isolation.

2. The long run

The half marathon is the first distance where the long run stops being one session among several and becomes the session the whole week is built around. Its job is not to simulate race day, it is to teach your body to keep producing energy aerobically for two-plus hours, to keep glycogen and fat-burning systems efficient under fatigue, and to toughen the tendons and connective tissue that absorb 21.1 km of impact. Grow it patiently, no more than about 10 percent further than your last long run of similar length, and keep it easy. A long run raced in training is a long run you need days to recover from, not one that builds you.

3. Lactate threshold

Threshold is the speed you can hold for roughly an hour, and for most recreational runners half marathon race pace sits just below it. One threshold session a week, tempo running or cruise intervals at a controlled hard effort, raises the ceiling you can sustain, so the same effort on race day buys a faster finish. This is the sharpening layer, and it sits on top of the base, not instead of it.

Sequence matters

Base and long run first, threshold second. A fast threshold session on top of a thin base just adds fatigue you cannot recover from before the next long run. Runners who improve fastest build these in order, not all at once.

04 / The week

How to structure a half marathon training week

The shape of a strong half marathon week barely changes through the block. What changes is the length of the long run and the sharpness of the one hard session as race day gets closer.

For a runner training four to five days a week, the week looks like this:

Two or three easy runs in Zone 2, controlled by heart rate, fully conversational
One threshold session, tempo running or cruise intervals at a controlled hard effort
One long run, kept easy, the anchor of the whole week, building toward 18-20 km
Optional strides once or twice a week, 6 short accelerations after an easy run, for economy

Around 80 percent of total volume stays easy. The single hard session carries the intensity, and the long run carries the volume. Most self-coached runners get this balance wrong in one direction or the other, either turning easy days into moderate ones or skipping the long run when the week gets busy.

A sample week, mid-block

This is what a representative week looks like once the long run has grown past its starting point but before the final taper. Every duration is a range, not a fixed number, land anywhere inside it and the session did its job.

Day	Session
Monday	Rest or easy walkFull recovery, no running
Tuesday	Easy run, 40-50 minZone 2, conversational, plus 4-6 strides at the end
Wednesday	Threshold run, 40-50 min totalIncl. 20-25 min at threshold effort, comfortably hard
Thursday	Easy run, 30-40 minZone 2, relaxed, shorter than Tuesday on purpose
Friday	RestFull recovery before the long run
Saturday	Long run, 100-120 minZone 2 throughout, roughly 14-16 km depending on your pace
Sunday	Easy run or rest, 20-30 minOptional shakeout, skip it if Saturday left you flat

A representative mid-block week for a runner training four to five days. Your own paces should come from your zones, not a generic chart, use the calculator above and the Zone Calculator to find them.

05 / Race day

How long should your longest run be

Build the long run to about 18 to 20 km, two to three weeks before race day, then taper. You do not need to run the full 21.1 km in training. Reaching 18 to 20 km at an easy effort builds the aerobic durability and connective-tissue strength that carry you through the final kilometres on race day, without digging a fatigue hole you cannot climb out of before the start line.

Grow it in small steps, not big jumps. A long run that grows by more than about 10 percent from the previous week's longest is the fastest route to an overuse injury, especially in the final third of a block when fatigue is already accumulating.

Race day pacing and fueling

The fastest way to run a slow half marathon is to start fast. Going out even a few seconds per kilometre under goal pace feels effortless in the first 5 km and costs minutes in the last 5. Run the opening 5 to 8 km at goal pace or a touch slower, settle into rhythm through the middle, and if anything is left, spend it in the final 5 km. An even or slightly negative split beats going out hard and hanging on, almost every time.

The half marathon is also the shortest distance on this list where fueling genuinely matters. Once you are racing for 75 minutes or longer, your glycogen stores start to run thin before the finish. Most runners do well with 30 to 60 grams of carbohydrate per hour once past the one-hour mark, taken as gels, chews, or sports drink, alongside water at aid stations. The rule that matters more than the exact numbers: never try a new fueling product or plan for the first time on race day. Practise the exact gels, timing, and drink on at least two of your longest training runs first, so your gut and your plan are both proven before it counts.

06 / The mistake

The mistake most half marathon runners make

Running the long run too fast and the easy days too hard. When every run drifts into the grey zone, a moderate effort that is too hard to build the base and too easy to build speed, the long run stops building durability and starts accumulating fatigue instead. The result shows up as a plateau in training or, worse, as the wall at 16 km on race day.

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The half marathon within the full framework

The half marathon is not a separate kind of training. It is the Run Mastery 5-step framework applied to one distance: zones, base, long run and threshold, race-day execution, and testing to see if it worked. The base makes the pace sustainable, the long run builds the durability to hold it, threshold sharpens it, and testing tells you whether the block is actually working.

It is the same structure behind every distance. If you are stepping up or down, the faster 10K guide sharpens the same systems at a higher intensity over a shorter distance, and the long run guide goes deeper on the single session that decides this one more than any other.

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Half Marathon FAQ

How long does it take to train for a half marathon?

If you can comfortably run 8 to 10 km, plan on 10 to 14 weeks. If you are starting from less, build a base to that point first, then begin the block. The half rewards endurance built through weeks of consistent aerobic running, not a compressed effort.

What pace should I run my half marathon at?

Your half marathon race pace is your goal finish time divided by 21.1. Aim to hold that pace evenly, or run the first 5 to 8 km a few seconds slower than goal pace and let the middle miles even out. Starting fast is the most common way to fade in the final 5K.

How long should my longest training run be before a half marathon?

Most runners build the long run to about 18 to 20 km, two to three weeks before race day, then taper. You do not need to cover the full 21.1 km in training. Reaching 18 to 20 km at an easy effort builds the durability that carries you through the final kilometres.

Do I need to fuel during a half marathon?

If you will be racing for 75 minutes or longer, yes. Most runners benefit from 30 to 60 grams of carbohydrate per hour once past the one-hour mark, taken as gels, chews, or sports drink. Practise your exact race-day fueling on at least two long runs before the race, never for the first time on the day.

Your next step

Put it to work.

A strong half marathon is built from more than the long run. The next step is making the whole week point toward race day.

1-on-1 coaching Build your half marathon. → Apply for 1-on-1 coaching and get a half-marathon week set around your goal pace, race date, and life. Keep learning Make the long run count. → Build duration without running every long run too hard. Keep learning Use intervals well. → Add the quality work that makes race pace sustainable. Free guides Browse all guides. → Find the next useful part of the Run Mastery method.