Health⏱ 5 min read
How to Calculate and Increase Your Weekly Running Mileage Safely
The 10% rule is the most widely cited guideline in running — and the most misapplied. Here's how to calculate weekly mileage increases that minimise injury risk without stunting progress.
Running injuries are predominantly overuse injuries — the result of increasing training load faster than the body can adapt. Understanding how to calculate sustainable progression is as important as any training method.
The 10% Rule and Its Limitations
The 10% Rule: increase weekly mileage by no more than 10%/week
Week 1: 30km
Week 2: 33km (+10%)
Week 3: 36.3km (+10%)
Week 4: 39.9km (+10%)
This works reasonably at moderate mileage.
Problems:
- At low mileage (10km/week), 10% = 1km — almost nothing
- At high mileage (80km/week), 10% = 8km — may be too much
- The rule ignores intensity — a 10% mileage increase at
higher intensity is a much larger training load increase
The 4-Week Pattern: Build-Build-Build-Recover
A more effective structure:
Week 1: 30km (base)
Week 2: 33km (+10%)
Week 3: 36km (+10%)
Week 4: 27km (-25%, recovery week)
Week 5: 38km (resume building from week 3 level)
The recovery week:
- Allows musculoskeletal adaptation to catch up with cardiovascular fitness
- Reduces injury risk significantly compared to continuous building
- Does NOT undo fitness — aerobic adaptations last 2-3 weeks at minimum
Acute:Chronic Workload Ratio (ACWR)
More sophisticated than the 10% rule.
ACWR = Acute Load (this week) / Chronic Load (4-week rolling average)
Safe zone: 0.8 - 1.3
Danger zone: above 1.5 (injury risk rises significantly)
Example:
Week 1-4 loads: 30, 33, 36, 27 km
4-week average (chronic load): (30+33+36+27)/4 = 31.5 km
Week 5 planned: 38 km
ACWR = 38 / 31.5 = 1.21 ✓ (safe zone)
Week 5 as 45 km: ACWR = 45 / 31.5 = 1.43 ✓ (borderline)
Week 5 as 50 km: ACWR = 50 / 31.5 = 1.59 ✗ (danger zone)
Long Run as a Percentage of Weekly Mileage
Your long run should be 25-35% of weekly mileage.
Above 40% concentrates too much load in one session.
At 40km/week: long run = 10-14km ✓
At 60km/week: long run = 15-21km ✓
At 80km/week: long run = 20-28km ✓
Marathon training: long runs eventually reach 28-35km,
which at 40% max means weekly mileage of 70-88km at peak.
This is why 40-50km weeks are insufficient marathon base for sub-4 hr goals.
What Counts Toward Weekly Mileage
Count everything that involves running biomechanics: easy runs, tempo runs, intervals, long runs. Do not count cycling or swimming as running mileage — cross-training doesn't stress the same structures. Treadmill mileage counts the same as outdoor (minimal biomechanical difference at equivalent speeds).