Running Shoe Replacement Calculator

The penalty begins above 150 lbs. Every 20 lbs over that threshold removes 5 percent of the shoe's base lifespan — at 170 lbs you lose 5 percent, at 190 lbs 10 percent. Weighing 150 lbs or less applies no weight adjustment at all.

Track surfaces are softer and more uniform than pavement, so the engine multiplies lifespan by 1.1 for track running while cutting it to 0.85 for trail. Road is the reference surface at 1.0, so track is the only option that pushes the estimate above the shoe type's base figure.

Yes, they are two views of the same number. Cost Per Mile divides a fixed $130 shoe price by the estimated Shoe Lifespan, so any input that shortens lifespan (heavier weight, trail surface, minimal shoe) raises the per-mile cost by exactly the same proportion.

Shoe Type, when compared the way this calculator's own sensitivity check compares inputs: a like-for-like probe around your current settings, not a full-range swing. Nudging Weekly Mileage by 10 percent in either direction moves Weeks Until Replace by roughly 18 percent at the default inputs, while switching across the full Neutral/Stability/Minimal spread moves it by roughly 35 percent — nearly double. It's true that mileage can swing further if you compare extreme values (say 10 vs. 40 miles a week) against shoe type's fixed 3-option range, but that comparison isn't apples-to-apples: it lets one input roam its entire domain while holding the other to its own bounded set of choices. Judged consistently, Shoe Type has the larger effect.