Jumping from a 5K to a half marathon doesn’t just mean running more miles. It changes the whole game—how you train, how you fuel, even how you think.
Here’s what I’ve learned personally (and what the research backs up) when making that leap from 3.1 to 13.1 miles.
Weekly Mileage Goes Up—But Don’t Overdo It
Let’s be real: you’re gonna be logging more miles. For a 5K plan, most beginners top out around 20 to 25 miles per week.
Once you shift into half marathon mode, expect to build toward 25 to 35 miles a week. That’s still beginner-friendly, but the increase matters—especially the long run, which can make up 25 to 30% of your weekly volume (according to Runners World).
The key? Patience. Stick with the 10%-per-week rule when increasing mileage. And every three or four weeks, cut your mileage back by about 20% to give your body a break.
Trust me, those “cutback weeks” saved me from burning out more than once.
The Long Run Becomes the Backbone of Training
With a 5K, your longest run might be 5–6 miles. But for the half, the long run is the centerpiece.
You’ll want to slowly build it up to 10–12 miles, or around 90–120 minutes. These runs aren’t just physical—they teach your body how to burn fat efficiently, stretch your endurance, and prep your brain for race day pacing.
5Ks rely more on short bursts of speed and glycogen stores, but half marathons demand steady energy over time.
One thing I always tell newer runners: once you’re comfy running 10 or 11 miles at an easy pace, you’re ready to go the full 13.1. You’ve already done the hard part.
From Speedwork to Stamina Workouts
Training for a 5K? You probably focused on interval workouts and VO₂ max work—things like 400m repeats at faster-than-race pace.
That stuff’s still useful for a half, but now the focus shifts. You’ll want to sprinkle in longer tempo runs—think 20–40 minutes at a comfortably hard pace—and longer intervals that hover around your half-marathon effort.
Why? Tempo work helps you push your lactate threshold higher, so you can run faster, longer, without crashing.
I still throw in the occasional fast repeat, just to stay sharp—but those sustained efforts at a “tough but manageable” pace? That’s where real half-marathon strength is built.
Fueling and Recovery Get Serious
Here’s the deal: you can probably get through a 5K without worrying much about mid-run fuel. Not so with a half.
Once your long runs cross the 60-minute mark, you’ll want to start eating and hydrating on the go.
- Carbs: 30–60 grams per hour (that’s one or two gels, depending on brand)
- Fluids: 16–24 ounces with electrolytes during longer sessions
Recovery also needs to step up. After long runs, I recommend a 3:1 carb-to-protein snack within 30–60 minutes to kickstart muscle repair.
I’ve skipped this step before and paid the price—legs trashed, energy gone, and dragging through the next workout.
Skip fueling, and you’ll likely hit that dreaded wall around the 80–90 minute mark when glycogen runs dry. Trust me: mid-run fuel isn’t “extra”—it’s survival.
The Mental Game Changes Completely
A 5K is basically a sprint you hold for 20–30 minutes. It hurts, but it’s short.
A half marathon? Totally different beast. You can’t rely on adrenaline alone—you’ve got to have a pacing plan and mental strategies.
Your pace will likely be 30–60 seconds slower per mile than your 5K effort. But it’ll feel tough in a different way: more grind, less pop.
One of my favorite tricks: break the race into chunks. I tell my runners, “Don’t think about 13.1 miles. Just get to the next mile marker. Then the next aid station.”
And when the going gets ugly, use mantras. My go-to? “Calm… steady… strong.”
It’s like mental duct tape holding everything together.