About this tool
Increasing weekly running mileage too fast is one of the leading causes of overuse injury. The 10 percent rule, popularized by coaches like Joe Henderson, suggests increasing mileage by no more than 10 percent per week. This calculator builds a week-by-week plan from your current to your target mileage at the rate you choose, including a suggested recovery week every 3 to 4 weeks.
How it works
Recovery week = previous week mileage x 0.75
Enter your current weekly miles and a target. The calculator multiplies each week by your chosen rate until the target is reached, capping at the target. The recovery week reference shows where to back off if you train more than 3 weeks in a row.
Heart rate zones and training science
Max heart rate (HRmax) is the upper bound your cardiovascular system can sustain for short bursts. The simplest estimate is the Fox formula: HRmax = 220 - age. Better is the Tanaka formula: HRmax = 208 - 0.7 x age, which is more accurate for adults above 40. Both are population averages with ±10 bpm individual variance.
Training zones (% of HRmax)
| Zone | % HRmax | Effort | Use |
|---|---|---|---|
| 1 Recovery | 50-60% | Very easy chat pace | Active recovery between sessions |
| 2 Endurance | 60-70% | Conversational | Aerobic base; 70-80% of weekly volume should be here |
| 3 Tempo | 70-80% | Comfortably hard, short sentences | Lactate threshold work, 30-60 min |
| 4 Threshold | 80-90% | Hard, breathing labored | VO2 max intervals, 3-8 min reps |
| 5 Anaerobic | 90-100% | All out | Sprints, 20-90 seconds |
1RM strength formulas
One-rep max (1RM) is the maximum weight you can lift once. Multiple-rep estimates:
- Epley: 1RM = weight x (1 + reps / 30)
- Brzycki: 1RM = weight x 36 / (37 - reps) - more accurate for 1-10 reps
- Lander: 1RM = weight x 100 / (101.3 - 2.67123 x reps)
Reps above 12 lose accuracy across all formulas. For periodized training, use 5-rep max (5RM) as a working metric and recompute every 6-8 weeks.
Pace, distance, time triangle
Endurance training revolves around three numbers - any two give the third:
- Pace = Time / Distance
- Time = Pace x Distance
- Distance = Time / Pace
Common race times and required paces (km):
| Event | Sub-elite | Recreational | Beginner |
|---|---|---|---|
| 5K | 20:00 (4:00/km) | 30:00 (6:00/km) | 40:00 (8:00/km) |
| 10K | 42:00 (4:12/km) | 60:00 (6:00/km) | 80:00 (8:00/km) |
| Half marathon | 1:35 (4:30/km) | 2:15 (6:24/km) | 3:00 (8:32/km) |
| Marathon | 3:30 (4:58/km) | 4:30 (6:24/km) | 5:30 (7:49/km) |
VO2 max ranges (ml/kg/min)
| Age | Elite men/women | Average men/women | Sedentary men/women |
|---|---|---|---|
| 20s | 75 / 65 | 44 / 38 | <35 / <30 |
| 30s | 70 / 60 | 42 / 36 | <33 / <28 |
| 40s | 65 / 55 | 39 / 33 | <31 / <26 |
| 50s | 60 / 50 | 36 / 31 | <28 / <24 |
| 60s | 55 / 45 | 33 / 28 | <26 / <22 |
Frequently asked questions
What is the 10 percent rule?
The 10 percent rule is a long-standing guideline in running coaching: increase weekly mileage by no more than 10 percent compared to the previous week. This gradual progression reduces overuse injury risk.
Should I take a recovery week?
Yes. Most coaches recommend reducing volume by 20 to 30 percent every 3 to 4 weeks to allow tissues to consolidate adaptation. The plan accommodates this by repeating progressive weeks.
What if I miss a week?
After 7 days off, restart at roughly 80 percent of your previous mileage. After 2 weeks off, drop to 50 percent. After 3+ weeks, treat yourself like a beginner and rebuild.
Is the 10 percent rule strict?
No. Beginners often add larger absolute increases (a few miles per week) early on, while experienced runners may safely increase by less than 10 percent. Listen to your body and back off if you feel persistent fatigue or pain.
How accurate is the 220-age formula?
Within about ±10 bpm for most adults. For people over 40, the Tanaka formula (208 - 0.7 x age) is closer to actual lab-measured HRmax. The only way to know your true HRmax is a maximal effort test - sprint until exhaustion.
Should I train mostly hard or mostly easy?
Mostly easy. Elite endurance athletes spend 70-80% of training time in zones 1-2. The polarized model (mostly easy + a small dose of very hard) consistently beats the threshold-heavy approach for long-term improvement.
How often should I retest my 1RM?
Every 6-8 weeks at most. True 1RM attempts are stressful and require taper. Most periodized programs use 3-5RM as a working number and recompute 1RM via the Epley or Brzycki formula.
What is heart rate variability (HRV) and why does it matter?
HRV is the variation in time between heartbeats. Higher HRV indicates better recovery. Track it via Whoop, Oura, Garmin, or Polar. Drops of 10%+ from your baseline often signal under-recovery or illness onset.
How do I know if I'm overtraining?
Signs: elevated resting heart rate, drop in HRV, sleep disruption, persistent fatigue, plateau or regression in performance, increased injuries. Reduce volume 30-50% for 1-2 weeks and monitor.
How accurate is the Running Mileage Base Calculator?
It applies the standard formula. Accuracy is limited only by your input precision. For decisions with material consequences (taxes, medical, legal, structural), use the result as a starting point and verify with a qualified professional in the relevant field.
Is the Running Mileage Base Calculator free to use?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads around the tool but not inside the calculation flow.
Are my inputs saved anywhere?
No. All inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but the analytics never see what you type into the form.
Can I use the Running Mileage Base Calculator on my phone?
Yes. The tool is responsive and tested on iOS Safari, Android Chrome, and major desktop browsers. Touch targets meet Apple's 44pt and Google's 48dp minimum.
Does the Running Mileage Base Calculator work offline?
Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.
How do I report a bug or suggest improvement to the Running Mileage Base Calculator?
Email hi@3tej.com with the URL of this page and a description of what you saw vs expected. We typically respond within 72 hours.
Can I share results from the Running Mileage Base Calculator?
Take a screenshot or copy the output. The page doesn't generate shareable URLs for specific calculations - inputs stay in your browser only.
Why are the results different from another running mileage base tool?
Most likely: different formula assumptions, different default values, different rounding rules, or different applicable rates. Check the methodology if both tools document it. Both can be valid for different scenarios.