Training
10K to Half Marathon: The 8–12 Week Jump
Going from 10K to half marathon means doubling your race distance — the biggest proportional jump in road running. It takes 8–12 weeks: one long run growing about a mile a week to a 10-mile peak, fueling practice (this is the distance where mid-race carbs start mattering), and the patience to leave your other runs alone.
Why this jump is different from 5K-to-10K
The 5K-to-10K bridge is mostly about patience. The half adds two genuinely new problems: fueling — you’ll be out there long enough that glycogen becomes a plot point — and time on feet, where the last miles stress tendons and form in ways an hour-long run never does. Community threads agree on the window: r/C25K’s consensus says 8–12 weeks is reasonable, and r/Marathon_Training treats 12 weeks as comfortable from a real 10K base.
The build, week by week
- Weeks 1–3: long run goes 7 → 8 → 9K (or 4.5 → 5 → 5.5 miles). Everything else stays put: two easy 30–45 minute runs.
- Week 4: hold flat. Consolidation weeks are where the adaptation actually lands.
- Weeks 5–8: 10K → 7 miles → 8 miles → hold. Start practicing race fueling on anything over an hour.
- Weeks 9–10: 9 miles, then the 10-mile confidence line. If you can run 10 easy, you can race 13.1.
- Weeks 11–12: taper — cut long-run distance roughly in half, keep a little speed, arrive bored and springy.
The three rules that protect the build
- The long run stays conversational — distance is the workout, not pace.
- Fuel every long run over an hour; race day is a rehearsal, not a premiere.
- If something hurts for two runs in a row, trade a run for rest — a missed week costs less than a missed block.
Book it before you build it
Twelve weeks from now is a real date — put a bib on it. Halfs appear in 1,217 of the races on our calendar: filter your city’s list to half marathon, aim for the fall cluster (October is peak season), and set your target with the pace chart. Then read the race-week checklist when it gets real.
Quick answers
How long does it take to go from 10K to half marathon?
8-12 weeks for most runners with a comfortable 10K. Eight weeks works if your 10K is genuinely easy; twelve gives margin for missed weeks and a proper taper. The variable that matters is how your long run absorbs growth, not your 10K speed.
Do I need to run 13.1 miles before the race?
No. Peaking at 10-11 miles is standard — the 10-mile long run is the confidence line. Taper freshness and race-day energy close the gap. What you should practice at full distance is fueling, not mileage.
Should I fuel during a half marathon?
Yes — most runners benefit from taking in carbs (a gel or chews) around 45-60 minutes in. Practice it on your long runs first; race day is the wrong time to discover a gel disagrees with you.
Published 2026-07-21 · RunFinders