Half Marathon (13.1 mi / 21K) Training Plan Length Calculator
If you're training for a 13.1-mile half marathon (21K), the first question is simple: how many weeks do you actually need? It depends almost entirely on where you're starting. A true beginner running 0-10 miles per week should plan for 16-20 weeks — basically a couch-to-half progression that builds an aerobic base before any serious workouts. An intermediate runner who already logs 15-25 miles per week and has finished a 5K or 10K can prep in 12-14 weeks. An experienced runner holding 30+ miles per week year-round can sharpen for a peak half marathon in 10-12 weeks. These ranges come straight from the most cited US coaching frameworks: Jack Daniels' Running Formula, Hal Higdon's Novice/Intermediate plans, Pete Pfitzinger's faster-times prep, and the Hansons brothers' cumulative-fatigue model. Most of them sit on an 80/20 polarized split — roughly 80% of weekly mileage in easy Zone 1-2 conversational pace and 20% in Zone 4-5 threshold and VO2max work. Volume should climb no faster than the 10% rule (10% more mileage week-over-week, then a 20-30% cutback every 3-4 weeks). Peak weekly volume lands around 25-40 mi for a first-time finisher, 35-50 mi for an intermediate chasing a PR, and 50-65+ mi for an advanced runner racing under 1:30. This calculator gives you the week count for your background. Updated 2026-05-28.
When to use this calculator
- First half marathon — couch-to-half runner needing a full base-build before race-specific work
- Intermediate runner using a 13.1-mile cycle as a stepping stone toward a Boston Qualifier marathon build
- Masters runner (40+) planning a conservative taper and lower peak mileage with more recovery between hard sessions
- Post-injury return — rebuilding from 0 mpw after a stress reaction, IT band issue, or plantar fasciitis layoff
- Experienced sub-1:30 runner sharpening fitness in a short 10-12 week block after a marathon
- Coach validating a client's plan length against Hal Higdon Novice 1, Pfitzinger 12-wk, or Hansons Beginner programs
Calculation Example
- Intermediate runner, 18 mi/wk current volume, goal half marathon
- Plan length: 14 weeks
- Peak mileage week 11: ~42 mi (67 km), long run 12 mi
How it works
3 min readHalf marathon training is built around four phases. Get the phasing right and the plan length almost picks itself.
Phase 1 — Base building (8-10 weeks for beginners, 3-4 weeks for advanced)
This is pure Zone 2 conversational running. Heart rate roughly 65-75% of max, pace where you can speak in full sentences. The goal isn't speed — it's mitochondrial density, capillary growth, and ligament/tendon adaptation. Add mileage at no more than the 10% rule per week. Every 3rd or 4th week, cut back 20-30% so tissues catch up. A beginner ends base at 18-22 mpw; an intermediate ends at 25-30 mpw; an advanced ends at 40-45 mpw.
Phase 2 — Build (4-6 weeks)
Now you layer in lactate threshold work. The two workhorses:
Phase 3 — Peak / race-specific (2-3 weeks)
Workouts now mimic the race. Goal-pace long runs (8-13 mi with the last 4-6 mi at half marathon pace), Pfitzinger-style 10-mile tempo + 2 mi easy, or Hansons strength sessions (6×1 mi at HM pace + 10 sec). Long run progression for a beginner climbs from 4-5 mi week 1 to 12-13 mi in the peak block. Intermediate caps long run at 14-15 mi; advanced can go 16 mi.
Phase 4 — Taper (1-2 weeks)
Greg McMillan's standard taper drops volume 30-40% across the last 14 days while keeping intensity — that means 3-4 short race-pace strides or a 20-min tempo two days before race day. Cutting intensity along with volume is the #1 reason runners feel sluggish on race morning. Beginners taper 7-10 days, advanced taper 10-14 days.
Workout types in a typical week
US plans worth copying
Pace targeting with VDOT
Daniels' VDOT system converts any recent race result into training paces (E easy, M marathon, T threshold, I interval, R repetition). A 25-min 5K = VDOT 49, which gives T-pace 6:38/mi, M-pace 7:25/mi, and predicted HM 1:44. Train at the paces VDOT prescribes, not at your goal-race pace, until the last 3 weeks.
Race-day fueling
Shoes
For the race, carbon-plated super shoes (Nike Vaporfly/Alphafly, Adidas Adios Pro, Saucony Endorphin Pro) show a 2-4% running economy improvement in lab data (Hoogkamer et al., 2017, Sports Medicine, PubMed PMID 29143929). They're race-day tools — too soft and unstable for daily training. For everyday miles, rotate 2-3 pairs of training shoes and retire them at 300-500 mi based on midsole compression, not appearance. Heavier runners and slower paces wear shoes out faster.
Final notes
Plan length is a planning tool, not a guarantee. Skipping the base phase is the most common mistake — runners jump straight into tempos and intervals because they're more exciting, then break down at week 6 with a soleus strain. If you're rebuilding from injury or coming back after a layoff, add 4 weeks to whatever your background says. Reviewed 2026-05-28.
Frequently asked questions
How long should I train for my first half marathon?
If you're starting from couch (0-10 mi/wk), give yourself 16-20 weeks. The first 8-10 weeks are pure base-building at Zone 2 conversational pace — no tempos, no intervals — just building the aerobic engine and ligament strength to tolerate 25-40 mpw without breaking down.
Hal Higdon vs Jack Daniels — which plan should I use?
Hal Higdon Novice 1 if you want a plug-and-play 12-week beginner plan with set distances. Jack Daniels' VDOT-based plan if you've already run a recent 5K or 10K and want training paces precisely calibrated to your fitness. Higdon is easier to follow; Daniels gives more performance per mile but assumes you'll calculate paces from vdoto2.com.
Should I only wear carbon-plated shoes on race day?
Yes for most runners. Hoogkamer 2017 found a 2-4% running economy improvement from Vaporflies, but they're soft, unstable, and wear out fast — typically 100-150 race miles. Train in stable everyday shoes (Brooks Ghost, Saucony Ride, Nike Pegasus), do 1-2 workouts in your race shoe over the final 4 weeks to acclimate, and save the rest for race day.
What pace should my long run be?
60-90 seconds per mile slower than goal half marathon pace, in Zone 2 — conversational, nose-breathing if possible. If your goal HM is 8:30/mi (1:51 finish), long run cruise pace is 9:30-10:00/mi. The last 2-4 miles can drop toward HM pace on race-specific long runs in the peak block.
Why do I feel sluggish during taper?
You cut intensity along with volume. The Greg McMillan taper drops volume 30-40% but keeps intensity — short race-pace strides, a 20-min tempo 4 days out, sharpening intervals. Pure rest makes legs feel flat. If you're doing taper right, you should feel slightly antsy and crisp, not heavy.
Should I run every day?
Beginners shouldn't — 3-4 run days plus 1-2 cross-training days protects tendons and bones. Intermediate runners can handle 4-5 run days. Only advanced runners with years of base benefit from 6-7 days/week, and even then 1-2 of those are recovery jogs under 30 minutes. Daily running raises stress fracture risk in runners under 25 mpw.
What's my target heart rate at half marathon pace?
Roughly 85-90% of max heart rate, or Zone 4. If you don't know max HR, use the Tanaka formula (208 − 0.7 × age) rather than the old 220-age. A 35-year-old has max ~184 bpm; HM pace HR is ~156-166 bpm. The pace itself is more reliable than HR — heat, sleep, and caffeine all push HR up 5-10 bpm without changing actual effort.
Can I use this half marathon block to train for a marathon?
Yes — it's the standard build-up. Run the half marathon as a tune-up race at the end of your base + build phase, then add 8-10 weeks of marathon-specific work (longer long runs, marathon-pace miles, fewer intervals). Many BQ chasers race a half 8-10 weeks before the marathon to test pace and fueling.
How much weekly mileage do I need to peak at?
First-time finisher: 25-40 mpw is plenty. Intermediate chasing sub-1:50: 35-50 mpw. Advanced sub-1:30 runner: 50-65+ mpw. Beyond 65 mpw the injury risk curve steepens fast for non-elite runners — extra mileage gives diminishing returns vs. quality threshold work.
Sources and references
- Jack Daniels — Daniels' Running Formula (Human Kinetics, 3rd ed.) + VDOT calculator
- Hal Higdon — Half Marathon Training Programs (Novice, Intermediate, Advanced)
- Pete Pfitzinger & Philip Latter — Faster Road Racing: 5K to Half Marathon (Human Kinetics)
- Hansons Half Marathon Method — Luke Humphrey, Keith & Kevin Hanson
- Hoogkamer W. et al. (2017). A comparison of the energetic cost of running in marathon racing shoes. Sports Medicine.
- USATF Coaching Education Program — Level 1 & 2 Endurance