Chasing 1:45: a 12-week half-marathon journey

The goal

Target: half-marathon (21.1 km) in 1 hour 45 minutes.

• Average pace needed: 5:00/km (or 8:03/mile).
• What it demands: enough speed to hold sub-5/km for sustained periods, comfortable long runs at 5:30–5:45/km, and the consistency to train at intensities that feel uncomfortable at first.

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Pre-requisites

Before starting, you should meet at least one of these benchmarks:

• Current half-marathon PB: 2:00 to 2:10 (or a 5 km time of 20 min or under).
• Weekly mileage: 20 to 30 km (12 to 18 mi) over 4 to 5 days.
• Base: able to complete a 10 km run at a steady 5:45/km pace.

If you’re a few minutes slower, add a 4-week base-building block (gradual mileage increase, easy runs) before the 12-week plan.

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How the plan works

Workout type	Purpose	Typical pace / effort
Easy run	Build aerobic foundation, support recovery	5:45–6:15/km (conversational)
Tempo run	Raise lactate threshold (pace you can hold “comfortably hard”)	4:45–5:00/km (about 85–90% max HR)
Interval session	Develop speed and VO₂ max with short, fast repeats	4:00–4:20/km on work, easy jog recovery
Long run	Build endurance, train fat metabolism	5:30–5:45/km (steady, relaxed)
Recovery / cross-training	Allow adaptation, prevent overuse injuries	Light activity (cycling, swimming, yoga) up to 60 min
Rest day	Full reset	No structured activity

Pace ranges are guidelines. Adjust for how you feel, weather, and terrain. Perceived effort or heart-rate zones work fine.

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Weekly plan (12 weeks)

Week	Mon	Tue	Wed	Thu	Fri	Sat	Sun
1	Rest	Easy 5 km	Tempo 6 km (4:55/km)	Easy 5 km	Intervals 5×400 m @ 4:10/km + jog 200 m	Long 12 km @ 5:45/km	Rest or cross-train
2	Rest	Easy 6 km	Tempo 7 km (4:55/km)	Easy 5 km	Intervals 6×400 m @ 4:10/km + jog 200 m	Long 13 km @ 5:45/km	Rest or cross-train
3	Rest	Easy 6 km	Tempo 8 km (4:50/km)	Easy 5 km	Intervals 4×800 m @ 4:20/km + jog 400 m	Long 14 km @ 5:40/km	Rest or cross-train
4	Rest	Easy 7 km	Tempo 9 km (4:50/km)	Easy 5 km	Intervals 5×800 m @ 4:20/km + jog 400 m	Long 15 km @ 5:40/km	Rest or cross-train
5	Rest	Easy 7 km	Tempo 10 km (4:45/km)	Easy 5 km	Intervals 6×400 m @ 4:05/km + jog 200 m	Long 16 km @ 5:35/km	Rest or cross-train
6	Rest	Easy 8 km	Tempo 10 km (4:45/km)	Easy 5 km	Intervals 4×1200 m @ 4:25/km + jog 400 m	Long 17 km @ 5:35/km	Rest or cross-train
7	Rest	Easy 8 km	Tempo 11 km (4:45/km)	Easy 5 km	Intervals 5×1200 m @ 4:25/km + jog 400 m	Long 18 km @ 5:30/km	Rest or cross-train
8	Rest	Easy 9 km	Tempo 12 km (4:40/km)	Easy 5 km	Intervals 6×400 m @ 4:00/km + jog 200 m	Long 19 km @ 5:30/km	Rest or cross-train
9	Rest	Easy 9 km	Tempo 12 km (4:40/km)	Easy 5 km	Intervals 4×1600 m @ 4:30/km + jog 400 m	Long 20 km @ 5:25/km	Rest or cross-train
10	Rest	Easy 10 km	Tempo 13 km (4:35/km)	Easy 5 km	Intervals 5×1600 m @ 4:30/km + jog 400 m	Long 21 km @ 5:25/km	Rest or cross-train
11	Rest	Easy 8 km	Tempo 10 km (4:35/km)	Easy 5 km	Intervals 3×800 m @ 4:00/km + jog 400 m	Long 16 km @ 5:20/km	Rest or cross-train
12 (race week)	Rest	Easy 5 km	Tempo 6 km (4:30/km), cut in half	Rest	Intervals 4×200 m @ 3:55/km (sharp)	3 km shake-out run	Race day, half-marathon 1:45 goal

Shift days to fit your schedule, but keep the order of intensity (easy, hard, easy) within each week.

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Detailed workout descriptions

Easy run

5 to 10 km at a relaxed pace where you can hold a conversation. Stay loose through the shoulders, let the arms hang naturally, and focus on a steady rhythm. These runs are the backbone of aerobic development and the recovery from harder work.

Tempo run

Lift the pace you can sustain for about an hour. Warm up 1 km easy, run the middle at comfortably hard tempo pace, cool down 1 km easy. During the main segment, breathing should be hard enough that more than a few words feels like work.

Interval session

Short, intense bursts with recovery. Sharpen speed and expand VO₂ max. Start 1 to 2 km easy, alternate fast pace with jog recovery, finish with 1 km easy. A stopwatch or GPS keeps you honest. Aim for even effort across all repeats rather than negative splits.

Long run

Build endurance and train fat metabolism. Run 30 to 45 seconds slower than race pace, relaxed and controlled. On runs over 90 minutes, take a gel or sports drink every 45 minutes. Breaking the distance into 5 km chunks makes the mental load smaller.

Recovery / cross-training

Cycling, swimming, elliptical, yoga, or an easy walk. Keep sessions under 60 minutes.

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Notes and tips

• Progression: cap weekly distance growth at 10% to avoid overuse injuries.
• Listen to your body: persistent soreness means swap a hard workout for something easy or take an extra rest day.
• Nutrition: load carbs the night before tempo and interval days, drink consistently, and have a light carb snack 30 minutes before hard work.
• Mindset: each workout is one building block. Steady training beats occasional hard efforts.
• Pace zones: run a recent 5K or 10K time trial to set your easy, tempo, and interval paces. Beats generic formulas.
• Adaptive planning: if a week feels overwhelming, drop the long run by 10 to 15% but keep the key workout’s intensity.
• Mistakes to avoid:
  1. Running the long run too fast.
  2. Skipping easy days and burning out.
  3. Skipping warm-up and cool-down.
  4. Not tracking effort. A 1 to 10 effort scale is as useful as a watch.

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FAQ

Q: I missed a workout. Should I do it later in the week? A: If it was an easy run, swap for a short easy jog. If it was a tempo or interval, treat the week as recovery, keep the long run, and slot the missed session into the following week’s easy day.

Q: My paces feel too hard. Can I adjust? A: Yes. Use perceived effort: easy runs feel easy, tempos comfortably hard, intervals hard but sustainable. If the numbers are too aggressive, add 10 to 15 seconds per km and re-evaluate after a week.

Q: I’m prone to shin splints. How can I stay injury-free? A: Strength work (glutes, core, calves) twice a week, softer surfaces when possible, gradual mileage growth. Ice and foam-roll after hard sessions.

Q: Can I substitute a cross-training day for a run? A: Yes, especially if you’re fatigued or dealing with niggles. Pick a low-impact option that keeps the aerobic stimulus.

Q: What if I’m already running 30 km a week? A: Start at the higher end of the plan’s mileage, but keep the intensity distribution (about 70% easy, 20% quality, 10% long). Adjust easy distances upward gradually.

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Closing and workout suggestion

The real value of chasing 1:45 is what happens along the way. Each run teaches you something about your speed, your limits, and your capacity. The roadmap is here. What matters next is showing up, paying attention, and noticing progress when it appears.

To kick off the plan, run an easy 5 km (conversational pace), then 5 × 400 m intervals at 4:10/km with 200 m jog recovery, then a 2 km cool-down. That gives you a feel for both endurance and speed.

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References

• 1/2 Marathon 12 Week Beginner | running Training Plan | TrainingPeaks (Blog)
• 1/2 Marathon 16 Week Beginner | running Training Plan | TrainingPeaks (Blog)