How Much Do You Need To Train For A 100-Mile Ultramarathon?

Written by:

Jason Koop

CTS Head Ultrarunning Coach

Updated On

July 20, 2026

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How Much Do You Need To Train For A 100-Mile Ultramarathon?

Stop obsessing over weekly mileage. One of the most common questions we get is: “How much do you need to train for a 100 miles?” And a lot of runners then expect an answer expressed by distance. But weekly mileage is not the metric that determines whether you finish, nor whether you should sign up in the first place. Here’s the formula we use to determine whether a runner has the necessary training availability to successfully finish an ultramarathon.

Assumption: Training Volume Must Scale With Race Distance

Here’s the flawed logic that keeps aspiring ultrarunners on the sidelines: If marathon training takes 8 hours a week, then a 50-miler must take 16. Training for a 100-miler must take even more. That reasoning seems entirely sound, but it’s 100% wrong.

There is no linear relationship between marathon training volume and ultramarathon training volume. A 100-miler does not require twice the training of a 50-miler. A 50-miler does not require twice the training of a marathon.

Reality: Training Volume Stays Virtually The Same Regardless of Race Distance

After training thousands of runners for races ranging from 26.2 miles up to 200+ miles, CTS Coaches have clear evidence that most athletes train at a similar volume regardless of the competition distance they’re targeting. Training volume is most often limited by real life – jobs, family priorities, social commitments, etc. There’s also an upper limit to the amount of training an athlete can absorb, recover from, and adapt to. Exceeding that volume leads to negative consequences (e.g., injury, burnout, maladaptation) rather than improved fitness, resilience, and performance.

Are there exceptions? Sure. Some athletes have all the time in the world to train and they’ve won the genetic lottery that enables them to absorb tremendously high levels of training stress. Pro athletes and very experienced ultrarunners also build resilience and durability through years of cumulative training and can therefore sustain high-volume training without injury.

The key point is that although higher training volume is one of the best ways to become a faster and more durable ultrarunner, that volume is best achieved through consistent training month after month and year after year. High weekly mileage isn’t the cornerstone of effective ultramarathon training. Highly consistent training – stacking weeks and weeks of sustainable training volume – is what counts.

Reframing the “How Many Miles?” Question

The question isn’t, “How many miles per week do I need?” The real question is: Can I hit the minimum volume threshold that develops the fitness required to reach the finish line?

CTS Ultrarunning Head Coach, Jason Koop, developed a concept to answer this question and described it in his book, “Training Essentials for Ultrarunning”. He calls it the minimum-maximum: the minimum amount of training time you need available during your period of highest training volume.

Defining Your “Minimum-Maximum” For Ultramarathon Training

Your “minimum-maximum” is not your average weekly volume across the whole training cycle. Nor is it your longest training week. Rather, it is the amount of training volume you need to be able to complete during the highest-volume training block before your goal race. Based on a typical ultramarathon periodization plan, this period comes about 6-9 weeks before your goal race.

Measure Ultramarathon Training Volume In Hours, Not Miles

Training Volume Required for Typical Ultramarathon Race Distances

To train for the following distances, your minimum-maximum needs to be:

• For a 50K or 50-mile ultramarathon: 6 hours per week for at least 3 consecutive weeks, starting 6 weeks before your goal event.

• For a 100K or 100-mile ultramarathon: 9 hours per week for at least 6 consecutive weeks, starting 9 weeks before your goal event.

Hitting the minimum-maximum isn’t a guarantee of success. But in our coaching experience, failing to achieve these levels of training volume in these critical timeframes is a reliable predictor of underperformance and potentially a DNF.

Outside of those key weeks, you can train at lower volume and still succeed, as long as your training is structured and intentional. A key component of your annual training plan should be to adequately prepare for this focused period of higher training volume. That means physically building up to the point you can absorb elevated training stress, training your gut to handle higher daily calorie intake for weeks at a time, and negotiating your work, family, and social priorities so you can commit to weeks of higher-volume training without causing conflicts.

What If You Can’t Commit To Your Minimum-Maximum?

One of the most valuable aspects of the “mimum-maximum” concept is helping to define realistic goals and objectives. Training for an ultramarathon can be a process that lasts months or even years. Before you commit to all the work required, and tie your hopes and dreams to a far-off goal, ask yourself the following questions (based on the distance you’re targeting):

Can I commit 6 hours per week for 3 weeks? Can I commit 9 hours per week for 6 weeks?

• YES: Great! You have every reason to believe you can do this.
• NO: Okay. That’s not a failure. It just means the distance you’re considering may not be right for you right now. Choose a different distance, build toward it, and come back when the timing is right.

Why Hours Matter More Than Miles

Most marathon and middle-distance runners track training by distance: miles logged, weekly totals, peak mileage weeks. On flat roads, that metric works reasonably well. Ultramarathons are typically run on trails and some feature massive elevation changes, so mileage becomes nearly irrelevant.

A 10-mile trail run in the mountains can take twice as long as a 10-mile road run and creates a fundamentally different stress on your body. Terrain, elevation, and technical demands all change the equation.

Basing training volume on hours instead of miles provides a better way to evaluate training stress. That’s why the minimum-maximum is expressed in time, not distance. Rather than chasing a mileage number on a GPS watch, you’re accumulating time on feet and time-at-intensity. This is what developed the aerobic fitness, durability, and fat oxidation capacity that a 100-mile race demands.

What to Do With the Training Time You Have

Whether you are a Time-Crunched Ultrarunner or a runner with all the time in the world available for training, what you do with your training time matters. The following principles apply no matter how much time you’re working with:

• Every session needs a purpose. Hard days hard, easy days easy.
• Protect your long run. Individual long runs don’t move fitness very much, but consistent long runs month after month are a key component of building the durability needed for ultramarathon success. If something has to give in a particular week, keep your long run and skip or shorten your shorter workouts.
• Volume is still the primary driver of adaptation. On a monthly and yearly basis, training volume is great predictor of ultramarathon progress. More running is better, as long as you can absorb the training stress. The minimum-maximum is a guideline to ensure you have a training block with enough cumulative volume to prepare for your goal event. If you can train more and recover from it, you should.
• Make your training look like your race as the event approaches. Your training should progress from generalized conditioning to race-specific work over the months leading up to your goal event. In the final two months or so, the following gain even more important: Time on feet on terrain that resembles the course. Practicing fueling and hydration during long efforts. Running in conditions that simulate race day.

The Simple Message

You probably don’t need as much training time as you think. You need enough — and enough has a specific number.

• 6 hours for 3 weeks, starting about 6 weeks before a 50K or 50-miler.
• 9 hours for 6 weeks, starting about 9 weeks before a 100K or 100-miler.

Miles are less important than hours for ultramarathon training. Stop counting miles, start counting hours, make them count.