How Many 20-Mile Runs Before a Marathon? Proven Marathon Training Tips

Wondering how many 20-mile runs you should squeeze in before race day? You're not alone. Most marathon training plans stick that 20-miler in there because it's the sweet spot—long enough to test your endurance but not so brutal that it wrecks you for weeks. But do you really need to crank out a pile of them, or is one enough?

The old-school crowd used to swear by three or four 20-mile runs in the weeks before a marathon. Now, a lot of pro coaches say you can get the same benefits with just two, sometimes even one if you’re coming in with good base fitness. It all depends on your goals—and how your body handles longer distances. Beginners usually stick to one or two, while more seasoned runners might do three, spaced out every other weekend.

Don’t just pick a number and force it; listen to your body. Going too far too often can backfire and leave you limping to the start line. The quality of your long runs, and how you bounce back from them, matter more than just stacking up long distances for bragging rights. Keep reading and I’ll break down how to pick the right number for you, tips for recovery, and what to watch out for when the miles start adding up.

• Why 20 Miles Is the Magic Number
• How Many 20-Mile Runs Do You Really Need?
• The Role of the Long Run in Training
• Signs You Need to Adjust Your Long Run
• How to Recover from 20-Milers
• Mistakes to Avoid Before Race Day

Why 20 Miles Is the Magic Number

Ever notice how almost every marathon training plan out there builds up to a 20-mile run? There’s a reason for that. Hitting 20 miles checks several crucial boxes—both physically and mentally. While the marathon is 26.2 miles, jumping straight up to that distance in training isn’t realistic for most bodies. Twenty miles is far enough to push your endurance limits, but not so far that you can’t show up healthy on race day.

Here’s what makes the 20-miler stand out:

• You get a real taste of race-day fatigue without totally wrecking your muscles or immune system. This gives your body time to recover and adapt.
• Your energy systems adapt. Running 20 miles trains your body to burn fat more efficiently, which is critical for the final miles of a marathon.
• The mental side is huge—if you can run 20 miles, those last 6 in the marathon feel less scary. Confidence plays a big role when things get tough out there.
• You learn the logistics of long runs: how to fuel, hydrate, pace yourself, and handle bathroom stops. By the time race day rolls around, you’ve ironed out the rookie mistakes.

Some coaches point to data showing injuries ramp up sharply when runners attempt full marathon distance in training. That’s why most stop at 20 and count on race-day excitement to carry them those last few painful miles. Here’s an idea of how race prep mileage typically ramps up close to the end (for folks following an 18-week plan):

Bottom line: The 20 mile run is like a dress rehearsal. It helps your body, gut, and brain get ready for that big 26.2, minus the injury risk of running the whole thing before game day.

How Many 20-Mile Runs Do You Really Need?

This is the million-dollar question for anyone diving into marathon training. Do you need one, two, three, or should you just skip them altogether? Most popular plans—like Hal Higdon’s or Hansons—recommend between one and three 20 mile run workouts before race day. If you look at elite runners, you’ll often see them doing even longer runs, but regular folks don’t need to go there.

Here’s what usually makes sense for most everyday runners:

• First-timers: One or two 20 mile run efforts are plenty. Your main goal is to get through the race healthy, not to destroy yourself in training.
• Experienced runners: Two or three can help boost your confidence and let you practice fueling and pacing across longer stretches.
• If you’re injury-prone or super busy, even 18 miles can give you similar benefits. It’s better to show up undertrained than broken.

Coaches like Greg McMillan and Jenny Hadfield agree—two 20 mile run workouts spaced out in your peak weeks (about every other weekend in the last 6-8 weeks before the big day) tend to work best for most people. Consistency with your weekly long run is way more important than hitting 20 miles over and over.

Don’t get hung up on a magic number. That last big long run is a tool, not a rule. You’re building confidence in your body and your training. If you train right, show up rested, and hit your long run with good energy a couple of times, you’re in a great spot for marathon day.

The Role of the Long Run in Training

Long runs are the heart of marathon training. They teach your body to keep going even when every part of you wants to quit. Most folks tackling their first marathon have never run close to 20 miles at once, so these key runs help you see what the distance actually feels like, both mentally and physically. It’s not just about pushing your legs for a long time—your muscles, bones, and even digestion all get a training session, too.

On a practical level, the long run helps you:

• Train your body to burn fat for energy after your stored carbs run low.
• Figure out what to eat and drink for a run that takes hours (because not every snack sits well over that distance).
• Build up the mental grit to keep moving when things get tough.
• Condition your muscles, joints, and bones to handle the pounding of race day.

There’s also a bunch of research showing that runners who hit their weekly long runs are way less likely to hit "the wall" during a marathon. Marathon-specific pace practice is another benefit—when you sprinkle a few miles at goal pace near the end of your long run, you train your brain and body to hold steady when tired. You don’t get that from shorter runs.

People sometimes forget that pacing matters. Going too fast on your long run can ruin the rest of your week, so most coaches recommend running slower than marathon pace, even up to 90 seconds per mile slower. This way, you save your best stuff for race day.

If you want to see typical data for runners building up to their first marathon:

So, the long run isn’t just a workout—it’s your dress rehearsal for marathon day. Use it to work out the kinks in your gear, nutrition, and pacing, and you’ll show up at the starting line a lot more confident.

Signs You Need to Adjust Your Long Run

Pushing through a 20 mile run is tough, but it's not supposed to leave you destroyed for days. If your body is throwing out warning signs, it's time to make some changes to your marathon training plan. Sometimes adding or taking away mileage—or tweaking your pace—can make all the difference.

Look out for these clear signs that your long runs need an update:

• Lingering fatigue: If you're still wiped out two or three days later, your run was probably too much for your current fitness level.
• Cranky joints or recurring pain: Sharp or dull pain in the knees, hips, or feet that sticks around could mean you're asking too much from your body. Healthy long runs shouldn’t come with new injuries.
• Consistently bad sleep: Struggling to get good sleep after your long run? Overdoing it can mess with your recovery and zap your immune system.
• Unusually slow recovery heart rate: If you wear a fitness tracker, notice if your resting heart rate stays elevated for 48 hours or more. That’s your body struggling to bounce back.
• No appetite or constant colds: Major drops in appetite or a sudden wave of minor illnesses can be your body’s way of telling you you’re overdoing the long run.

Mileage isn’t everything. Quality matters—not just distance. Studies tracking marathoners show that runners who get more than three long runs over 18 miles before race day are nearly 30% more likely to get injured compared to those who keep it to two or three solid long runs. Check out this quick stat:

Don’t be afraid to cut a long run short or pull back when you feel any of these signs. It’s smarter to skip a few miles than end up sidelined on race day. Trust your body—you’ll thank yourself at the finish line.

How to Recover from 20-Milers

Finishing a 20-mile run feels like a huge win—but what you do right after can make or break your next long run and your whole marathon training plan. Your muscles take a beating on those extra miles, so smart recovery is where real gains happen.

First things first, don’t just collapse on the grass. Keep moving for a few minutes to let your heart rate settle. Gentle walking and light stretching help flush out all that built-up junk from your muscles. Hydration comes next—replace the fluids you lost with water or an electrolyte drink. The classic rule: drink enough so your pee is light yellow by the end of the day.

Food matters more than you think. Experts agree you’ve got about a 30-minute window post-run for the best muscle repair. Go for something with carbs and a bit of protein, like a chocolate milk, peanut butter toast, or a banana with Greek yogurt. That combo helps your legs rebuild stronger for the next 20 mile run.

"A simple recovery snack after a long run can kickstart muscle repair and get blood sugar back to normal. It’s honestly as important as the run itself," says coach Jay Johnson, author of Simple Marathon Training.

Now, let’s talk about the next day. Most runners report that soreness peaks about 24 hours later. Easy movement is better than sitting still—go for a gentle walk, ride a bike, or try some yoga. And get more sleep than usual; real repair happens when you’re out cold.

If you’re curious about what a recovery week might look like, check this out:

For sore spots that just won’t quit, ice and compression gear can help. And don’t ignore little niggles—nipping them in the bud now is way easier than dealing with a blown-up injury close to race day. Prioritizing recovery after long runs isn’t extra, it’s just as crucial as knocking out those mileage milestones.

Mistakes to Avoid Before Race Day

Let’s talk about what not to do after you survive those 20 mile run long runs. Some mistakes seem obvious, but they trip up even seasoned runners. Here’s how to dodge the most common facepalms before your marathon.

• Pushing a final 20-miler too close to race day. Your last really long marathon training run should happen at least two to three weeks out. Anything closer, and you risk toeing the start line with sore muscles—not a good plan.
• Ignoring your taper. Backing off your volume is not optional. A proper taper boosts your freshness and lets your legs recover. Cutting mileage by about 20-30% each week pre-marathon works for most folks.
• Trying something new on race week. Don’t switch your shoes, change your breakfast, or start chugging new sports drinks. If you didn’t practice it during a long run, don’t gamble on it now.
• Skipping recovery. Following a big 20 mile run, prioritize rest, sleep, and plenty of carbs. Hydrate well and stretch, or you’re just asking for an overuse injury or sickness right when you need to stay healthy.
• Packing race gear at the last minute. Make a checklist a week ahead: shoes, socks, bib, gels, anti-chafe balm, and backup gear if the weather turns wild. Forget something major and you’ll spend race morning in panic mode.

How common are taper mistakes? According to a 2023 training survey from Marathon Handbook, about 35% of non-elite runners admitted to running too long or too hard during their taper. Those runners reported slower finish times and more aches on race day.

The best approach? Plan ahead, stick to familiar routines, and trust your marathon preparation. When in doubt, take it easier than you think—fresh legs are way more useful on race day than a few extra junk miles.