| Week | Distance | In the other unit |
|---|
What is the 10% rule?
The 10% rule is the best-known guideline for building running volume safely: don't increase your total weekly distance by more than about 10% from one week to the next. The logic is simple — your heart and lungs adapt to training faster than your tendons, ligaments, and bones, so ramping up too quickly is how most runners get injured.
Enter your current weekly distance above and this calculator projects a week-by-week build at the rate you choose, so you can see exactly where you'll be in a few weeks — and how long it takes to reach a goal.
Use cut-back weeks, not just constant growth
Increasing every single week eventually catches up with you. Most coaches build for two to three weeks, then take a cut-back week — dropping volume by 20–30% to let your body absorb the work before climbing again. This calculator flags a suggested cut-back every fourth week so you can plan them in.
The result is a saw-tooth progression: up, up, down, up — which builds fitness with far less injury risk than a straight line.
When the 10% rule bends
- Very low mileage: going from 10 km to 11 km is trivially safe — you can increase faster when volume is low.
- High mileage: at 100+ km/week, even 10% is a big jump; smaller increases are wiser.
- Coming back from a break: rebuild conservatively — you lose fitness faster than durability, so start lower than you think.
- Listen to the signals: niggles, poor sleep, or a rising resting heart rate mean hold or cut back, whatever the maths says.
Example: building from 40 km/week at 10%
| Week | Distance (km) | Distance (mi) |
|---|---|---|
| 1 | 40.0 | 24.9 |
| 2 | 44.0 | 27.3 |
| 3 | 48.4 | 30.1 |
| 4 | 53.2 | 33.1 |
| 5 | 58.6 | 36.4 |
| 6 | 64.4 | 40.0 |
In just six weeks a 10% build takes 40 km/week to over 64 km/week — which is exactly why cut-back weeks matter. Use the calculator to plan yours.
Let your plan handle the progression
The Running Genie builds your mileage progression, cut-back weeks, and workouts automatically — and adjusts them from your real training, so you build fitness without guessing.
Frequently asked questions
What is the 10% rule in running?
It says you should not increase your total weekly running distance by more than about 10% from one week to the next. Building volume gradually gives your muscles, tendons, and bones time to adapt, which lowers the risk of overuse injuries.
Is the 10% rule too conservative?
For very low mileage or returning runners, 10% can be slow. For higher mileage it can be aggressive. Treat 10% as a sensible default, not a law: many coaches prefer smaller increases with a cut-back week every third or fourth week.
What is a cut-back week?
A cut-back (or down) week is a planned reduction in mileage, usually every third or fourth week, where you drop volume by roughly 20–30%. It lets your body absorb the previous weeks of training and reduces cumulative fatigue before you build again.
How quickly can I safely increase my running?
A common approach is to build for two to three weeks, take a cut-back week, then continue. Increases of 5–10% per building week suit most runners. Persistent aches, poor sleep, or a rising resting heart rate are signals to hold or reduce volume rather than push on.
Does the 10% rule apply to time or distance?
Either works — many runners apply it to weekly distance, but you can apply the same 10% guideline to total weekly running time, which is often better for trail and hilly running where pace varies. This calculator uses distance, but the principle is identical.
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Build mileage the smart way
Download The Running Genie for a plan that ramps your mileage safely, schedules cut-back weeks, and adapts to how your training is actually going.
