AI-built half marathon training plan
12-16 weeks, 4-5 sessions/week. Progressive long runs to 18-22 km, long threshold tempo (35-45 min), race-pace simulations. EntrenAI calibrates everything to your VDOT and applies precise taper for race-day PR.
Updated
What is a half marathon training plan?
The half marathon (21.0975 km) is the sweet spot between speed and endurance: long enough that aerobic base is decisive (60-120 minutes of running), short enough to race near threshold (~85-92 % VDOT). Trained on three pillars:
- High weekly aerobic volume (60-90 km/week for intermediates)
- Progressive long runs reaching 18-22 km in build block
- Long tempo runs (30-45 min at threshold pace)
Unlike 5K/10K, half marathon introduces race-pace simulations of 14-16 km in the specific block. The dominant adaptation is sustained lactate threshold — the ability to hold pace just below threshold for 90-120 min.
The paces you get, by goal
Every half marathon goal has a VDOT (Daniels) and from it come the five paces the app writes every session with: easy (E), marathon pace (M), threshold (T), intervals (I) and repetitions (R). Find your goal in a column and you have the exact paces you will see in your plan.
| Half in 2:15 | Half in 2:00 | Half in 1:40 | |
|---|---|---|---|
| VDOT | 31.7 | 36.5 | 45.1 |
| Easy (E) | 7:40 /km | 6:53 /km | 5:49 /km |
| Marathon pace (M) | 6:29 /km | 5:48 /km | 4:54 /km |
| Threshold (T) | 6:08 /km | 5:29 /km | 4:37 /km |
| Intervals (I) | 5:39 /km | 5:03 /km | 4:15 /km |
| Repetitions (R) | 5:15 /km | 4:41 /km | 3:57 /km |
| Equivalent to 5K · 10K | 29:19 · 1:00:56 | 26:04 · 54:07 | 21:46 · 45:07 |
Your AI-generated plan
1. Prerequisite check. EntrenAI requires a minimum base:
- Beginner: running 25-30 km/week comfortably + completed a previous 10K
- Intermediate: running 40-50 km/week + regular quality tempos
- Advanced: running 60+ km/week + regular VO2max intervals
Don't meet the base? The plan recommends an 8-week 10K plan first, then start the half.
2. Target pace. Half marathon pace is roughly 8-12 seconds/km slower than 10K pace. For someone with 10K at 45:00 (4:30/km), half ~4:38-4:42/km → 1:38-1:39:00.
3. Progressive long run. Grows +1 km every 2 weeks until 18-22 km in build block. Critical: the max long run never exceeds 30 % of weekly volume — if you run 60 km/week, max long run is 18 km, not 22 km.
4. Long tempo runs. 25 min in base block, 30-35 min in build, 40-45 min in specific. Can be continuous or split into 2×20 min with 2 min jog.
5. Typical weekly structure (5 sessions, intermediate):
- Easy 1: 8-10 km
- Quality 1: cruise intervals or VO2max intervals
- Easy 2 + strides: 8 km
- Quality 2: continuous tempo or long with tempo finish
- Long run: 16-22 km
6. Validated taper (10-14 days). 50-60 % volume reduction, keeps 1-2 short quality sessions. Carb-loading in the 2-3 days pre-race.
How the kilometres climb over the 14 weeks of the plan
From 40 to 72 km per week, with a deload every fourth week and 2 taper weeks. The thin bar is the long run, which reaches 22 km.
- Base
- Build
- Specific
- Taper
- Deload
- Long run
Who is this plan for?
- My first half (beginner). 14-16 weeks, 4 sessions/week, 35-50 km/week. Focus on building long runs and aerobic endurance. Goal: comfortable finish, 2:00-2:30.
- PR my half (intermediate). 12-14 weeks, 4-5 sessions/week, 50-70 km/week. Long tempo + simulations focus. Typical improvement 5-10 min.
- Sub-1:30 / sub-1:20 (advanced). 12 weeks, 5-6 sessions/week, 70-100 km/week. Double quality session/week in build block.
How to run half in 2:00: the splits
The most expensive mistake in a race is going out fast. The plan teaches you the opposite: first 20% at 2% slower than goal pace, middle section on pace, last 20% slightly faster. This is what the watch reads at each point.
| Point | Segment pace | Elapsed time |
|---|---|---|
| km 5 | 5:47 /km | 28:54 |
| km 10 | 5:41 /km | 57:19 |
| km 15 | 5:41 /km | 1:25:43 |
| km 20 | 5:38 /km | 1:53:52 |
| Finish (21.1 km) | 5:36 /km | 2:00:01 |
Your first weeks, in detail
Week 9
Intermediate build — VDOT 50 (half target 1:35:00, pace 4:30/km)| Day | Session type | Detail | Duration |
|---|---|---|---|
| Monday | Easy | 12 km Z2 at 5:00/km. | 60 min |
| Tuesday | Cruise intervals | 15 min warm-up + **6×1500 m at 4:15/km (Threshold) with 60s jog** + 10 min cool-down. Total ~14 km. | 70 min |
| Wednesday | Easy + strides | 9 km Z2 at 5:00/km + 6×100 m strides. | 50 min |
| Thursday | Long tempo | 15 min warm-up + **35 min @ 4:25/km (between Threshold and half-marathon pace)** + 10 min cool-down. Total ~14 km. Key session. | 65 min |
| Friday | Recovery | Rest or 5 km very easy Z1. | 0-25 min |
| Saturday | Easy | 8 km Z2 at 5:00/km. | 40 min |
| Sunday | Progressive long run | 20 km at 5:00-5:15/km for the first 12 km, then 4:30/km for last 8 km (target pace). Hydration + 2 gels. Key session of the week. | 105 min |
Week 13
Advanced specific — VDOT 58 (half target 1:18:00, pace 3:42/km)| Day | Session type | Detail | Duration |
|---|---|---|---|
| Monday | Easy + strides | 14 km Z2 at 4:20/km + 6×100 m strides. | 65 min |
| Tuesday | Half simulation — extended target pace | 20 min warm-up + **2×6 km at 3:42/km (half target pace) with 5 min jog between blocks** + 10 min cool-down. Total ~22 km. Key block session. | 90 min |
| Wednesday | Easy | 11 km Z2 at 4:30/km. | 50 min |
| Thursday | VO2max + tempo | 20 min warm-up + **5×1000 m at 3:20/km with 90s rest + 10 min @ 3:42/km (half pace)** + 10 min cool-down. Total ~17 km. | 75 min |
| Friday | Recovery | 8 km Z1 at 4:55/km. | 40 min |
| Saturday | Easy with strides | 11 km Z2 at 4:25/km + 8×100 m strides. | 50 min |
| Sunday | Long run with long tempo | 23 km Z2 at 4:25-4:35/km with km 14-20 at 3:50/km (slightly slower than target pace). Block max accumulation. | 105 min |
These examples are real extracts from the EntrenAI planning engine. Your personal plan adjusts to your level, equipment and availability.
Equipment needed
EntrenAI automatically substitutes any exercise if you don’t have the gear.
- Training shoes + carbon-plated shoes ONLY for race and specific simulations
- GPS watch with HR, >10h battery (Garmin Forerunner 265+, COROS Pace 3)
- Chest HR strap (Polar H10, Garmin HRM-Pro)
- Gel belt + handheld water bottle for long runs
- Gels (min 4-6 per long run >18 km), sports drinks
- Foam roller + bands + percussion massager for recovery
- Recommended: race-day weather-appropriate gear (summer vs winter)
What most people get wrong (and how to avoid it)
- 1
Long runs that are too long
Common belief: 'to run 21K well I need to do a 25 km long run'. False. Max long run shouldn't exceed 30 % of weekly volume. If volume is 60 km/week, max is 18 km. Excessive long runs produce accumulated fatigue that degrades next week's quality sessions — worse adaptation, higher injury risk.
- 2
Skipping race-pace simulations
6-12 km simulations at race pace in the specific block are crucial. Without them, you reach race day having never felt target pace for more than 4-5 km. Uncertainty raises RPE and you almost always lose time in the last 5 km. EntrenAI prescribes progressive simulations (3 km, 6 km, 8 km, 10 km) every 7-10 days in specific block.
- 3
Increasing volume in the last 14 days
Taper is sacred: -50-60 % volume in the last 10-14 days. Many people panic ('I'll lose fitness') and train more during taper. Result: heavy legs on race day. Taper supercompensation produces 1-3 % performance improvement (a couple minutes on a 1:30 half).
- 4
Trying new shoes or gels on race day
Universal experienced-runner rule: **nothing new on race day**. No shoes, gels, breakfast, gear. Everything must have been tested in at least 2 prior long runs. Otherwise = high risk of GI issue, blister, chafing or equipment failure.
- 5
Not training in race-day heat / cold
If the half is in July and you always train at 7am, you won't be heat-adapted to race conditions (temperature climbs at 9am). The last 4 weeks, EntrenAI prescribes 2-3 sessions at the approximate event time, in similar temperature/humidity.
- 6
Going out too fast in the first half
Universal tactical mistake in half marathon. Adrenaline + pack + 'I feel good' = first 5 km at 10K pace. Result: dead from km 14, last 7 km are torture. Optimal strategy: first 10 km at target pace or 1-2 seconds slower, second 11 km at target pace or slightly faster if feeling good.
- 7
Carb loading done wrong
Classic 3-day load with 7-10 g/kg carbs (Bergström, 1967) is still valid but underused. Many runners load only the day before (insufficient). Others load too many days with fat and protein (slow digestion, discomfort). EntrenAI prescribes the exact menu for the 3 days pre-race based on your bodyweight.
Other Running plan variants
Back to the general Running plan
- AI-built 5K training planA 5K plan tuned to your real VDOT, with track intervals, tempo runs and a long run over 3-5 sessions a week. From a first sub-30 5K to sub-18.
- AI-built 10K training planA 10K plan tuned to your real VDOT: long tempo runs, VO2max and threshold intervals and a weekly long run. From a sub-60 first 10K to sub-37.
- AI-built marathon training planA marathon plan calibrated to your real VDOT: long runs up to 32 km, threshold tempo, race-pace simulations and a validated taper over 16-24 weeks.
- AI-built beginner running planA beginner running plan that takes you from sedentary to a comfortable 5K in 10-14 weeks with a progressive run-walk method, 3 sessions a week.
- AI-built sub-50-minute 10K planA 12-week plan to run 10K in under 50 minutes at 4:50/km, built on threshold work, 1 km intervals and a progressive long run. For 55-60 minute 10K runners.
- AI-built sub-2-hour half marathon planA 14-16 week plan to run your half marathon under 2 hours at 5:41/km, with threshold work, tempo runs and an 18-22 km long run. For sub-55 10K runners.
- AI-built running plan for weight lossA running plan for weight loss that combines Z2 running, two strength sessions a week and a moderate calorie deficit over 12-16 weeks, injury-free.
Frequently asked questions
14-16 weeks from a base of 25-30 km/week and a previous 10K. Coming from sedentary, first a 5K plan (12 weeks) → 10K (8 weeks) → half (14 weeks) ≈ 8-10 months total. Trap: many new runners jump to a half plan after a 5K and get injured weeks 6-8 from unadapted volume.
Approximations: half 2:00+ → 14-16 km. half 1:45-2:00 → 17-19 km. half 1:30-1:45 → 19-21 km. half sub-1:30 → 20-23 km. The 30 % weekly volume rule is strict: don't exceed it.
Roughly 1 gel every 25-30 min of running. For 1:30 race: 3-4 gels. For 1:45: 4-5 gels. For 2:00+: 5-6 gels. More important than quantity: it must be exactly the brand you've tested in prior long runs. And first one from km 5-6, NOT from the start (digestion).
Recommended if chasing a PR (>3 % efficiency improvement, ~3 minutes on a 1:40 half). NOT necessary to finish or enjoy. The two dominant brands (Nike Vaporfly/Alphafly, Adidas Adios Pro) cost €250-300. Asics Metaspeed, Saucony Endorphin Pro and New Balance SuperComp Elite are valid alternatives with carbon plate.
For beginners/intermediates: 2-3 per year (with 4-5 months between). For advanced: 3-4 per year (with 3 months between). Racing 1 half per month is excessive — body doesn't recover and you never peak correctly. After each half, minimum 7-10 days active recovery + 2-3 weeks reduced volume.
No. A half plan has max long run 22 km and tempo runs of 35-45 min. A marathon plan has long runs up to 32-35 km and much higher weekly volume (80-110 km/week for sub-3). The half plan optimizes for 21K-specific adaptation (sustained threshold), the marathon plan optimizes for 42 km metabolic endurance.
Yes. 2 strength sessions/week improve economy 3-5 % and prevent injuries. Important: separate heavy strength at least 24h from long run (deadlift Friday + long run Sunday is OK; deadlift Saturday is NOT). In taper, the last 2 weeks drop strength to 1 very light session.
Depends on the injury. Mild (3-4/10 discomfort): EntrenAI substitutes 50 % running with bike/elliptical for 7-10 days. Moderate (5-7/10): full pause 7 days + gradual return. Lose 14+ consecutive days, usually need to reschedule the half or adjust target time more conservatively.
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