If you’re training for a marathon, there’s one question that almost every runner eventually asks:
How long should my longest run actually be?
Do you need to run 30 kilometres?
32 kilometres?
35 kilometres?
Should you run for three hours?
And if you’re expecting your marathon to take five hours, how can a three-hour training run possibly prepare you for race day?
The answer isn’t as simple as picking a magic distance.
Your long run needs to be long enough to prepare you for 42.2 kilometres—but not so long that recovering from it compromises the rest of your training.
That balance is where smart marathon training comes in.
Why Is the Long Run So Important?
Your long run is one of the most important sessions in marathon preparation.
It develops your aerobic endurance and improves your ability to keep moving efficiently as fatigue builds.
It also develops something that becomes increasingly important during the marathon: durability.
You’re teaching your body to continue running when your legs are no longer fresh.
But the benefits aren’t purely physical.
Long runs give you opportunities to practise:
- Fuelling and hydration
- Running in your race-day shoes and clothing
- Pacing and intensity control
- Mental strategies for extended periods of running
- Your pre-run breakfast and preparation
- What to do when things don’t feel perfect
Long runs are where many of the lessons you’ll use on marathon day are learned.
Do You Need to Run 42.2 Kilometres Before Your Marathon?
For most runners, no.
You don’t need to prove you can run a marathon before running your marathon.
Remember that a training run is completed in the middle of a training programme.
You don’t have a taper beforehand.
You may have trained the previous day.
And you need to recover quickly enough to continue training afterwards.
Running the full 42.2 kilometres during training can create a huge recovery cost without necessarily providing enough additional benefit to justify it.
Your marathon itself is where all the pieces come together.
Training prepares you for that moment.
Is 32 Kilometres the Magic Number?
You’ve probably heard that every marathon runner needs to complete a 20-mile—or approximately 32-kilometre—long run.
It’s become one of marathon training’s traditional milestones.
And there’s nothing inherently wrong with 32 kilometres.
Research examining marathon training has found an association between longer peak training runs and faster marathon performances, although that doesn’t mean every athlete needs exactly 32 kilometres.
The problem comes when runners start treating 32 kilometres as a compulsory box that must be ticked regardless of their ability.
For a faster runner, 32 kilometres might take two-and-a-half hours.
For another runner, it could take four hours or considerably longer.
Those are very different training stresses.
That’s why I prefer looking at time as well as distance.
Distance Doesn’t Tell the Whole Story
Imagine two athletes both completing a 30-kilometre long run.
Runner A finishes in 2 hours 30 minutes.
Runner B takes 4 hours.
They’ve covered exactly the same distance.
But they haven’t completed the same workout.
Runner B has experienced another 90 minutes of impact, muscular fatigue, energy expenditure and time on their feet.
That’s why simply prescribing the same maximum distance to every marathon runner doesn’t make sense.
Your training needs to reflect you, not somebody else’s Strava account.
What About the Three-Hour Rule?
You’ll often hear runners say that your long run should never exceed three hours.
There’s some sound coaching logic behind limiting very long training runs: eventually the additional benefit has to be weighed against increasing fatigue and the recovery required afterwards.
Jack Daniels, whose training principles have strongly influenced my own approach to periodisation, recommends limiting the longest steady run to around 150 minutes, while allowing longer durations for athletes combining running and walking.
Other respected coaches take a different approach.
Some argue that a runner expecting to spend four, five or more hours completing their marathon can benefit physically and psychologically from occasionally spending longer on their feet.
This disagreement highlights an important point:
There isn’t a magic duration that works for everybody.
So How Long Should Your Long Run Be?
I prefer to think about your long run as something that develops progressively throughout your marathon programme rather than obsessing over one enormous session at the end.
Your long run might initially be 60–90 minutes.
As your training develops, that gradually increases.
The appropriate peak depends on your:
- Running experience
- Current training volume
- Expected marathon time
- Injury history
- Ability to recover
- Training consistency
- Goal for the event
A runner chasing a fast marathon and consistently completing substantial weekly mileage has very different needs from someone preparing to complete their first marathon in five or six hours.
The important thing is that the long run is appropriate for the athlete completing it.
Your Long Run Shouldn’t Destroy the Following Week
Here’s one of my favourite ways of judging whether a long run was appropriate.
Ask yourself:
What happened afterwards?
Being tired after a long run is normal.
But if you’re so exhausted that you can’t train properly for several days—or you’re carrying soreness and niggles throughout the following week—then the session may have created more fatigue than your body was ready to absorb.
One monster long run isn’t going to make your marathon.
Months of consistent training will.
I’d rather see you complete a slightly shorter long run, recover well and continue training than smash out an impressive distance and lose the next week.
Don’t Race Your Long Runs
Another common mistake is turning the weekly long run into a performance test.
You feel good.
Your pace gradually increases.
Then you decide to see how fast you can finish.
Suddenly your Level II long run has become a race.
Most of your traditional marathon long-run work should remain controlled at Level II.
That doesn’t mean every long run throughout your programme must be identical. Depending on your training phase and experience, there can be a place for structured faster running within selected long runs.
But intensity should be included because it has a specific training purpose.
Not because you felt good at 18 kilometres and decided to chase an impressive average pace.
Build Your Long Run Gradually
The safest and most effective long runs are generally the ones you’ve progressively prepared yourself to complete.
Don’t jump from 90 minutes to two-and-a-half hours because you’ve suddenly realised your marathon is getting close.
Your muscles, tendons, bones and cardiovascular system need time to adapt.
That’s why I like gradually increasing long-run duration—often by around 10–15% when appropriate—rather than making dramatic jumps.
And progression doesn’t need to continue every single week.
There can be shorter long runs and recovery weeks throughout the programme.
Training doesn’t need to form a perfectly straight line upwards.
Your Long Run Is Also Fuelling Practice
Once your long runs become substantial, they’re not just running sessions.
They’re also fuelling rehearsals.
You need to learn what you can eat and drink while running.
How frequently should you consume carbohydrate?
How much fluid works for you?
Which products does your stomach tolerate?
What happens after two hours?
These are questions you want answered during training—not at kilometre 30 on race day.
The longer runs within your marathon preparation provide some of your best opportunities to develop and refine that strategy.
Don’t Forget the Mental Training
There’s also enormous psychological value in long runs.
When you’ve been running for a couple of hours, you’ll experience moments where you’re uncomfortable, bored, tired or simply ready to stop.
Learning to remain calm and keep moving is valuable marathon preparation.
But you don’t need to run the full marathon distance to develop that confidence.
Every successful long run adds another piece of evidence:
I can do this.
As those sessions accumulate throughout your programme, confidence grows.
When Should Your Longest Run Be?
Your biggest long run shouldn’t be the weekend before your marathon.
You need enough time to recover and allow the training adaptations to occur before race day.
For many marathon programmes, the longest run occurs roughly three to four weeks before the marathon, followed by a taper that progressively reduces training volume while maintaining enough stimulus to keep you feeling sharp.
By that stage, the work is largely done.
You’re no longer trying to gain huge amounts of fitness.
You’re preparing to arrive at the start line able to use the fitness you’ve already built.
Don’t Measure Marathon Readiness by One Run
This might be the most important message in the entire article.
Your marathon preparation isn’t defined by whether you completed one particular distance.
It’s the accumulation of training that matters.
The Level II running.
The quality workouts.
The long runs.
The recovery.
The strength work.
The fuelling practice.
And, most importantly, the consistency.
You could complete a brilliant 32-kilometre training run and still arrive at your marathon poorly prepared if the rest of your training has been inconsistent.
Equally, you might never reach that traditional 32-kilometre milestone and still have an excellent marathon because you’ve put together months of appropriate, consistent training.
The Bottom Line
So, how long should your marathon long run be?
Long enough to develop the endurance and durability you’ll need on race day—but not so long that the recovery cost outweighs the training benefit.
There isn’t one perfect distance for every runner.
Don’t become obsessed with reaching 32 kilometres simply because somebody told you that’s what marathon runners do.
Look at the entire training programme.
Build your long runs progressively.
Keep most of them controlled.
Practise your fuelling.
Respect your recovery.
And remember that you don’t need to prove you can run 42.2 kilometres during training.
That’s what race day is for.
Take the Guesswork Out of Your Marathon Training
Knowing how far to run is only one piece of marathon preparation.
How quickly should your long run progress? When should you introduce quality work? How should your training change as race day approaches? And how do you balance all of that without simply accumulating more and more fatigue?
That’s where Marathon Mastery comes in.
Marathon Mastery gives you structured, progressive marathon training designed to help you build the endurance, durability and confidence you need for 42.2 kilometres—without relying on random workouts or trying to copy somebody else’s training.
Whether you’re preparing for your first marathon or looking to improve your next one, the goal is to arrive at the start line knowing you’ve done the right training at the right time.
Train with purpose. Build consistently. Arrive ready.