PACR
AI half marathon training plan, rebuilt every morning.
The half is long enough to punish a pace you cannot hold and short enough to reward the work you actually did. PACR sets the block from your race date, then rewrites each session on the morning you run it — around your last run, your real pace and the weather outside.
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How a half marathon block is built.
The half runs on threshold. Everything in the block either builds it, rehearses it, or protects the legs that have to hold it for ninety minutes.
Easy volume with one long run creeping past 14 km, plus strides twice a week. Nothing here is hard enough to be interesting, which is exactly why it works.
Threshold becomes the engine: 4 × 8 minutes with short floats, then 2 × 20 minutes, at a pace taken from your own sessions rather than a chart on a race-predictor site.
Race pace moves inside the long run — 16 km with 8 km at goal pace — plus one cut-down run a fortnight where the last 3 km are quicker than the first.
Volume comes down, one sharp session a week stays. Race-pace kilometres get short and clean so they feel rehearsed rather than raced.
What a half marathon week looks like.
A representative build week for a runner training four to six days. Two quality days, one long run, and easy days that stay easy.
Turn up flat on a Tuesday and the threshold session is shortened, not deleted — the plan reads the run you did on Sunday before it writes the one you do today.
What decides today's half session.
Rebuilt at 4am from three things: what you ran, what you can hold, and what the air is doing.
Your last run
Split drift, cadence and how hard the end felt. A long run that fell apart in the last 4 km changes Tuesday's threshold session before you have even seen it.
Your real pace
Half marathon pace sits close to, but not at, threshold. PACR models threshold from your own runs and sets the target off it in seconds, so it moves as your fitness does.
Today's climate
Heat, humidity and wind decide what your goal pace costs today. The session carries a heat offset so a humid Saturday changes the number instead of ruining the workout.
Threshold, without the watch-staring.
Threshold work goes wrong in the first ninety seconds, when it feels easy. The coach is loudest exactly there.
Half marathon training questions.
What runners ask in the twelve weeks before their first — or fastest — half.
How many weeks does it take to train for a half marathon?
Twelve to sixteen weeks if you already run regularly, and longer if you are building up from short runs. PACR sizes the block from your race date and your recent sessions rather than handing you a fixed template.
Can I train for a half marathon without running a marathon first?
Yes — most half marathon runners never run a marathon, and the half is not a stepping stone to anything. It is its own event, built on threshold running and a long run that tops out near race distance.
How long should my longest run be before a half marathon?
Somewhere between 16 and 21 km for most runners. PACR grows the long run from where yours actually is now, and shortens it in the week you turn up tired rather than in the week the template says to.
What pace should I run a half marathon at?
Close to threshold, but not at it. PACR models threshold from your own sessions and sets half marathon pace off that, adjusting the number as your fitness moves and as the weather changes what it costs.
Is this plan good for a first half marathon?
Yes. The block starts at your current volume, and on easy days the coach's main job is to slow you down — the run that gets a first-timer to the start line healthy is the boring one.
What if I can only run four days a week?
That is enough for a half. The plan places one long run and one or two quality sessions in the days you have, and stops trying to bolt filler mileage onto a week that will not hold it.
Training a different distance?
Same coach, same daily rewrite, different block.