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Half Marathon (13.1 mi / 21K) Training Plan Length Calculator

How many weeks to train for a 13.1-mile half marathon by background: beginner 16-20, intermediate 12-14, advanced 10-12. Jack Daniels VDOT + Hal Higdon based.

Data verified · June 2026
Edited by Martín Rodríguez
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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

Half Marathon Training Plan Reference by Runner Level

Runner Level	Weekly Mileage (baseline)	Plan Length	Peak Weekly Volume	Long Run Cap	Taper
Beginner	0–10 mi/week	16–20 weeks	25–40 mi	12–13 mi	7–10 days
Intermediate	15–25 mi/week	12–14 weeks	35–50 mi	14–15 mi	10–14 days
Advanced	30+ mi/week	10–12 weeks	50–65+ mi	16 mi	10–14 days

Fuente: Jack Daniels' Running Formula, Hal Higdon, Pete Pfitzinger & Hansons Half Marathon Method — as cited in hacecuentas.com/21k-training-plan-weeks (2026)

Half Marathon Goal Time → Required Race Pace (per km & per mile)

Even-pace splits for a half marathon (21.0975 km / 13.109 mi). This is the average pace you must sustain start to finish.

Finish time	Pace /km	Pace /mile	Speed (km/h)	Typical level
1:30:00	4:16	6:52	14.1	Advanced
1:45:00	4:59	8:01	12.1	Strong intermediate
2:00:00	5:41	9:09	10.5	Intermediate (popular target)
2:15:00	6:24	10:18	9.4	Improver
2:30:00	7:07	11:27	8.4	Beginner / first-timer
2:45:00	7:49	12:35	7.7	Beginner / run-walk

Exact arithmetic: pace/km = finish time ÷ 21.0975; pace/mile = finish time ÷ 13.109 (1 mile = 1.609344 km). Long runs go 60–90 s/km slower than goal pace; the sub-2:00 half (5:41/km) is the single most common amateur target.

How it works

Half 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:

Tempo runs: 20-40 minutes at Zone 3-4, roughly half marathon pace + 10 seconds/mile for beginners, or 10K to half marathon pace for advanced. Jack Daniels calls this T-pace and caps continuous tempo at 20 min for most athletes.

Intervals: 400-1600m repeats at Zone 5 / VO2max effort. Classic sessions are 6×800m at 5K pace with 2:00 jog, or 5×1000m at 3K-5K pace. Yasso 800s (10×800m, 2:00 rest) are popular because the average 800 time in minutes:seconds correlates loosely with predicted marathon time in hours:minutes — for the half, the rough estimate is half marathon = Yasso average ÷ 2.

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

Easy run (Zone 2): 60-75% of weekly mileage, fully conversational, 60-90 sec/mi slower than HM pace.

Tempo (Zone 3-4): lactate threshold, 1-2 mmol/L over baseline, the "comfortably hard" pace you could sustain ~1 hour racing.

Intervals (Zone 5): VO2max, all-out 3-6 min reps, equal jog recovery.

Long run (Zone 2 progressive): 25-30% of weekly mileage in a single session, capped at ~2:30 hours regardless of pace.

US plans worth copying

Hal Higdon Novice 1 (12 wk): lowest-volume option, 3 run days + 2 cross-train, peak 25 mpw. The default for first-timers.

Hal Higdon Intermediate (12 wk): 4 run days, peak 33 mpw, adds tempo and pace runs.

Pete Pfitzinger Faster Road Racing 12-wk 47 mpw plan: advanced, 5-6 run days, threshold + VO2max.

Hansons Half Marathon Beginner/Advanced: cumulative fatigue philosophy — never a true rest day, capped long run at 10 mi, 6 days/week.

Jack Daniels VDOT-based plan: uses your recent race time → VDOT score → exact training paces. Calculator at vdoto2.com.

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

Pre-race (3-4 hours out): 100 g carbs, low fiber, low fat. Bagel + banana + small coffee is standard.

During race: 30-60 g carbs per hour from gels or chews, 400-600 mg sodium per hour. Most runners take 1 gel at mile 4-5 and another at mile 8-9. Practice fueling on every long run — not race day.

Hydration: sip water at every aid station; replace 16-24 oz per hour in heat.

Post-race: 0.3 g/lb body weight of protein within 30 min plus carbs for glycogen resynthesis.

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.

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

14 weeks, peaking at ~42 mi/week

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 & references

Methodology & trust

Editorial

Sports calculator with its formula verified automatically against Jack Daniels — Daniels' Running Formula (Human Kinetics, 3rd ed.) + VDOT calculator, per our editorial policy and methodology.

Updates

Updated: June 2026. Parameters are verified periodically against the cited sources.

Privacy

Calculations run 100% in your browser. We do not store or transmit your data.

Limitations

Indicative results. For critical decisions, consult a professional.

📌 How to cite this calculator

Rodríguez, M. (2026). Half Marathon (13.1 mi / 21K) Training Plan Length Calculator. Hacé Cuentas. https://hacecuentas.com/en/21k-training-plan-weeks

Content licensed under CC-BY 4.0 — reuse it citing the source with a link to Hacé Cuentas.

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