Half Marathon Long Run Progression Distance, Pace, and Terrain

Your plan calls for a "long run," and you're trying to work out how far that actually needs to go before race day — and whether it needs to hit the full 13.1. Your longest training run should be 10-12 miles (16-19km) for most runners, done 2-3 weeks before race day — you do not need to run the full 13.1 miles in training. First-timers can cap at 9-10 miles; runners chasing a fast time can push to 13-14 miles. Below I cover how to adjust that number for hills, trails, and altitude, when splitting the run across two sessions actually works, and how the target shifts by experience level.

Get the terrain or pace adjustment wrong, though, and it rarely shows up as a bad run in the moment — it shows up two weeks later as a knee that won't settle down, or a long run you can't finish right when your taper should be starting. Most of the runners I coach who blow up this phase of training aren't undertrained; they're chasing a flat-road number on a hilly course, or stacking split sessions past the point where they still build real race-specific fatigue resistance.

Terrain-Specific Long Run Adjustments

Every ranking page on this topic assumes flat road running throughout. That's fine if you're training on flat roads. It's not fine if you're not, and most readers aren't.

On hilly terrain, cut your target distance by 10-15%, or switch to running by time-on-feet instead of chasing mileage. Allow 30-45 seconds per mile slower pace for every 100ft (30m) of climb in the route.

On trail long runs, reduce distance 15-20% versus the road-equivalent target, and expect 20-30% more time on feet due to technical terrain underfoot. At altitude above 5,000ft (1,500m), reduce your pace expectations by roughly 4-8 seconds per mile for every 1,000ft above that threshold, and prioritise time-on-feet over distance for the first 2-3 weeks of acclimatisation.

My direct guidance to athletes training for hilly-course races: stop watching pace entirely on long runs above 300ft of climb. Chasing a flat-course number on hilly terrain is the single biggest cause of long-run burnout I see in this phase of training.

Splitting Your Long Run Across Two Sessions

Time-crunched doesn't have to mean skipped. If you genuinely can't find one continuous window, splitting is a real option — but there's a floor and a cap on how far you can lean on it.

Keep each single session at a minimum of 5 miles — below that, the long run's aerobic stimulus is essentially lost. A roughly 60/40 split works well: for a 13-mile target, that's about 8 miles in the morning and 5 miles in the evening.

Here's the trade-off worth understanding: your combined split-session distance can run 10-15% higher than a single continuous session would allow, since fatigue resets between sessions. But splitting doesn't build the race-specific fatigue resistance a continuous run does, so cap it at no more than 2 of your final 6 long runs before race day.

One of my athletes, working shifts, split her long run into AM/PM sessions for 8 of 14 weeks under my plan and still hit her race goal — with that explicit cap in place for the final stretch.

Group vs. Solo Long Runs

Group long runs help some runners and hurt others, and it comes down to one honest question: does the group's easy pace actually match yours?

Group runs improve pacing discipline for runners who habitually go out too fast when running alone — the peer pace anchors you. But they raise injury risk for runners tempted to match a faster group's pace on what's supposed to be an easy day.

My rule: only run long runs in a group if the group's natural easy pace sits within 30 seconds per mile of your own prescribed easy pace. Outside that window, run solo or find a pace-matched partner instead.

Long Run Distance and Pace by Experience Level

Your long run pace should sit 60-90 seconds per mile slower than your half marathon goal pace, and it should make up 25-30% of your total weekly mileage. Here's how peak distance and structure shift across experience tiers.

Long Run Workout Structures

Beyond a plain easy-paced long run, three workout structures show up repeatedly in a well-built progression. Fast-finish: run the final 1-3 miles at or near half marathon goal pace. Progression: the first 60% of the run easy, the final 40% at half marathon goal pace. Mid-run tempo: a sustained tempo block inserted into the middle miles, easy pace either side of it.

For the complete session-by-session breakdown of when to use each, see structured long run workouts.

Treadmill Long Runs

Treadmill long runs need one adjustment and one management strategy. Set a 1% incline to replicate outdoor effort — a flat treadmill belt is measurably easier than outdoor running at the same pace.

Break the run into 2-3 mile blocks with small pace or incline changes between them to manage the monotony. For the full indoor progression guide, see treadmill long runs for half marathon training.

Frequently Asked Questions

Do I need to run the full 13.1 miles before race day?

No. Your longest training run should be 10-12 miles for most runners, done 2-3 weeks before race day. Race-day adrenaline and taper freshness cover the remaining distance.

How long should my longest training run be?

10-12 miles (16-19km) for most runners. First-timers can cap at 9-10 miles, while runners chasing a fast time can push to 13-14 miles.

How much should I increase long run distance week to week?

Roughly 1 mile a week is a sensible ceiling for most runners, in line with the broader 10% weekly mileage rule. Build in a cutback week every third or fourth week to let the increase actually absorb.

What pace should I run my long runs at?

60-90 seconds per mile slower than your half marathon goal pace, conversational throughout. Advanced runners add short goal-pace segments in the closing miles of some long runs.

When should I schedule my final long run before the race?

2-3 weeks out is the sweet spot. Any closer to race day and you're not giving your legs enough time to absorb and recover from it before you need them fresh.

Is it okay to take walk breaks during long runs?

Yes — planned walk breaks are a legitimate pacing strategy, not a failure. Read our full run-walk method guide for how to structure the intervals properly.

What should I do if I miss a scheduled long run?

Don't try to make it up by tacking extra distance onto the next one. Resume your normal progression from where the schedule currently sits — one missed long run rarely changes your race-day outcome.

How much of my weekly mileage should the long run make up?

25-30% of your total weekly mileage is the sensible range. Go much higher than that regularly and you're under-supporting the long run with the easy mileage that helps you absorb it.

More Pages on This Topic

Some Other Pages You May Like