How to Run a Sub 1 Hour 20
Half Marathon.

Pace, splits & training plan for a sub 1:20 half marathon.

What pace is a 1:20 half marathon?

A 1:20 half marathon is a pace of 3:48 per kilometre (6:06 per mile), or 15.8 km/h (9.8 mph).

Pace /km

3:48

min/km

Pace /mile

6:06

min/mi

Speed

15.8

km/h

Speed

9.8

mph

1:20 Half Marathon splits.

KM Cumulative Time
1 3:48
2 7:35
3 11:23
4 15:10
5 18:58
6 22:45
7 26:33
8 30:20
9 34:08
10 37:55
11 41:43
12 45:30
13 49:18
14 53:05
15 56:53
16 1:00:40
17 1:04:28
18 1:08:15
19 1:12:03
20 1:15:50
21 1:19:38
21.0975 1:20:00
Mile Cumulative Time
1 6:06
2 12:12
3 18:18
4 24:25
5 30:31
6 36:37
7 42:43
8 48:49
9 54:55
10 1:01:01
11 1:07:08
12 1:13:14
13 1:19:20
13.11 1:20:00

What does this pace feel like?

A 3:48/km average for the half marathon is a serious, advanced effort — quick enough that breathing is deep and rhythmic from the early kilometres and conversation is out of the question. The pace sits close to threshold, so the race rewards runners who have trained their body to clear lactate efficiently and who have the discipline to hold back through a fast first 10 km.

How to train for a 1:20 half marathon.

Build to 65–85 km per week. The cornerstone session is a weekly threshold run — 25–30 minutes continuous at 3:55–4:00/km, or broken as 3 × 10 minutes — plus one faster session such as 5 × 1600 m at 3:40–3:45/km with 2–3 minutes' recovery.

Long runs of 20–24 km should finish with intent: the final 5–6 km at race pace teaches your legs to run 3:48/km when they're already tired, which is exactly what the last quarter of the race asks. Easy mileage at 4:45–5:15/km fills the rest of the week.

From a sub-1:25 starting point, 12 weeks of focused work is realistic. A recent 10K around 36:00–36:30 confirms you're in range. In the final fortnight, drop volume by 30–40% but keep touching race pace so the rhythm stays familiar.

Adjust your target.

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Related.

Aiming faster?

Sub 1:15 Half Marathon Pace Guide

Training plans

Half Marathon Running Plans

Need more time?

Sub 1:30 Half Marathon Pace Guide
Back to Pace Calculator

FAQs.

Is a 1:20 half marathon good?

Yes — sub-1:20 requires 3:48/km (6:06/mi) for the full distance and is a benchmark that places you well inside the top few percent at most big-city half marathons.

What 10K time predicts a 1:20 half marathon?

Around 36:00–36:30. If your 10K is faster but the half keeps escaping you, the missing ingredient is usually weekly volume rather than speed.

How many weeks do I need to train for a 1:20 half?

From a 1:23–1:25 base, 12 weeks of structured threshold work and pace-specific long runs is a realistic timeline. From further back, allow a full season.