Running a half marathon under 1 h 45: pace, VMA and the 10-week plan
Under 1 h 45 for the half means 4:58 per kilometre for 21 km. It is the most common goal of regular runners, and one of the most accessible with structured preparation. Here is the VMA required, the central role of threshold, and how your AI coach builds the 10 weeks from your Garmin data.
Last updated: 2026-09-19
The VMA required
A half is run at about 85% of VMA. To hold 12.1 km/h for 1 h 45, you need a VMA of at least 14.2 km/h. With 15 km/h the goal becomes comfortable and 1 h 40 comes into view.
The coach reads your VMA, its date and source, and checks your longest run of the last 90 days: without a 75-minute run already done, it adds two base weeks before the plan.
Threshold, the half's key session
The 10-week plan raises threshold from 3 × 8 minutes to 30 continuous minutes, at about 4:45 per kilometre. It is this session that takes you from 1 h 50 to 1 h 45: it teaches you to hold a pace barely faster than race pace.
The long run climbs from 60 to 100 minutes, with the last 20 minutes at half pace from week 6.
Race day
Instruction: first two kilometres at 5:03, then a steady 4:58 to the 16th, then let go over the last five. Pass 10 km between 49 min 30 and 50 min. The watch carries the 4:55-to-5:01 range per segment.
- VMA of at least 14.2 km/h.
- Threshold up to 30 continuous min.
- Race day: 4:58 from the 3rd to the 16th kilometre, 10 km split at 50 min.
Water every 5 km is enough; a gel at the 12th kilometre if you tested it on a long run.
Frequently asked questions
I run 1 h 52, is it doable in one plan?
Yes if your VMA is 14.5 km/h or more: threshold is what is missing more than speed. Otherwise, a 10K plan to raise VMA, then the half plan.
How many sessions a week?
Three are enough with a VMA of 15 km/h. With 14.2 km/h, the four-session variant secures the goal.
Do you need to run 21 km before the race?
No: the longest run is 100 minutes, about 18 to 19 km. The race does the rest.
Ready to prepare for your half marathon?
Pick your race date and weekly session count: your AI coach builds the plan and pushes it to your Garmin.
Start the half marathon plan