The long run is the cornerstone of half-marathon training. It is also the workout that injures the most Indian runners I know - not because it is too long, but because it is too long too soon, too fast, or too repetitive. The question 'how long should my long run be' has a defensible answer. It just depends on where you are starting and what kind of half you want to finish.
Let me give you the framework I have used to coach a dozen friends through their first half. Three numbers. Three rules. One non-negotiable.
The short answer, and then the long one
Most runners can finish a half-marathon comfortably if their longest training run reaches 18-22 km. That is the consensus that emerges from coaching literature - Pfitzinger, Daniels, Hudson - and from our own training notes across Indian half marathon plans. But 'reaching 18-22 km' is the endpoint of a 10-14 week build, not the starting point.
The minimum: 16 km
If you do not run a long run of at least 16 km in the build, race day will hurt in unfamiliar ways past kilometre 12. The body has not been there. You are introducing a new physiological state in the middle of competition. Bad bet.
The standard: 18-20 km
Most coaching literature converges on a longest run of approximately 18-20 km for a 90 percent confident half-marathon finish. This is the volume that, combined with the rest of the weekly mileage, builds the glycogen stores, the joint conditioning, and the mental practice needed for 21.1 km.
The over-distance bet: 22-24 km
For runners chasing a time goal (sub-1:45, sub-1:30) or who want to feel particularly comfortable past 15 km, one or two long runs in the 22-24 km range are useful. They are not necessary. They do add injury risk if not built into a long enough base.
How to build to the long run
The structure matters as much as the endpoint.
The 10-percent rule applies, with deload weeks
Weekly long-run distance should increase by no more than approximately 10-15% week to week, with a deload week (typically a 25% drop in long-run distance) every fourth week. This is not a slogan; it is the load-management principle that prevents the most common Indian first-half injuries - shin splints, ITB issues, and stress reactions.
The build-up pattern
Starting from a long run of 8-10 km, the typical 12-week half marathon build looks like this: week 1 - 8 km, week 2 - 10 km, week 3 - 11 km, week 4 deload - 8 km, week 5 - 12 km, week 6 - 14 km, week 7 - 16 km, week 8 deload - 12 km, week 9 - 17 km, week 10 - 19 km, week 11 - 14 km (pre-taper), week 12 - race. Adjust by your starting point. Use our plan generator to build the week-by-week chart from your current base.
The deload week is not optional
I have watched runners skip deload weeks because they feel fine. They almost always pay for it in week 9 or 10. The deload is not a rest from the mileage - it is a chance for the bone, the connective tissue, and the immune system to catch up to the cardiovascular system, which adapts faster than everything else.
How fast should your long run be
Pace is where most half-marathon training plans go wrong.
The 80/20 principle
The 80/20 rule, popularised by Stephen Seiler's polarised training research, suggests that approximately 80% of weekly running time should be at easy aerobic intensity, with the remaining 20% at threshold or higher. The long run sits squarely in the 80%.
What 'easy' actually means
Easy pace for the long run is approximately 90-120 seconds per kilometre slower than your half-marathon goal pace. A runner targeting a 5:00/km half should be doing long runs at 6:30-7:00/km. A runner targeting a 6:00/km half should be doing long runs at 7:30-8:00/km. Conversational pace. The talk test: you can speak in full sentences without gasping. Faster than this is not better.
Mid-build race-pace miles
From week 7 or 8 of a 12-week build, adding 4-8 km of half-marathon goal pace to the back end of a long run (a 'fast finish' long run) is supported in the coaching literature. This teaches pacing under fatigue. See our types of run guide for the broader menu.
Indian context: where, when, what to carry
The where and when of the long run shape its quality more than the schedule does.
Routes
Long runs need quiet, runnable terrain. Around 18-22 km of city pavement in any major Indian city is grim. The runners who do well shift to: Cubbon Park-MG Road loops in Bengaluru, Marine Drive-Worli Sea Face in Mumbai, Lodhi-India Gate loops in Delhi, Sanjay Gandhi National Park trails in Mumbai's northern suburbs, Sabarmati Riverfront in Ahmedabad. Identify two long-run routes you trust. Rotate them.
Start time
Long runs in summer (March-June) should start by 5:00 a.m. in most of India. In winter (November-February), 6:00-6:30 a.m. is more humane. Monsoon long runs are a separate problem - read our heat and monsoon guide for the call-sheet.
Hydration and fuel
Any long run over 90 minutes needs on-the-run fuel. 30-60 grams of carbohydrate per hour, typically through gels, dates, or jaggery-and-sea-salt energy balls. Hydrate 200-300 ml every 20-30 minutes in moderate heat. Indian summer long runs can require an extra 500 ml. The nutrition pages have the full carb-and-fluid math.
What to do if you cannot reach 18-20 km
Things go wrong. Plans break. Here is how to recover.
Missing one long run
One missed long run is recoverable. Do not try to make it up the following weekend by jumping. Continue the next planned long run, then add 1-2 km the week after. The body does not respond well to abrupt over-distance.
Missing two consecutive long runs
Two consecutive missed long runs cost you about 2 weeks of progress. If your race is 4+ weeks away, you can still rebuild to 18-19 km safely. If your race is in 2-3 weeks, race conservatively or consider deferring.
Injury during the build
Pain during a long run that is sharp, localised, or worsening means stop. Do not finish the run. Walk home. Visit our calculators to recalibrate your goal once you have a clean return-to-run plan, and visit the Running Lab for the deeper reads on training load.
One last thing
The long run is also the workout that, more than any other, decides whether you finish your first half marathon enjoying running or quietly resenting it. Pick a starting distance you can actually run. Build slowly. Pace easy. Carry fuel. Eat after. Sleep more. The mileage is doing its job in the background, but only if you let it. That is the deal. Marathon plans work similarly but at a larger scale, if you decide the half is the start, not the finish.