How many miles are left in the pair by your back door? Almost nobody can answer that, and the runners who think they can are usually working from a number they half remember reading somewhere.
Shoes do not fail on a schedule. They fail unevenly, quietly, and mostly in the midsole where you cannot see it. So the useful question is not how far you have run in them, but what the shoes and your legs are telling you.
The mileage rule is a starting point, not an answer
The standard guidance is a few hundred miles, commonly quoted as somewhere in the range of 300 to 500 miles, or roughly 500 to 800 kilometres. It is a reasonable planning figure. Use it to decide when to start paying attention, not when to throw shoes away.
The reason it is weak on its own is that the same distance does very different amounts of damage depending on who is running it and where. Two runners can both log 400 miles in the same model and end up with midsoles in completely different condition. Mileage is an input. It is not a measurement of the shoe.
Signal one: the midsole stops springing back
This is the best single check, and it takes ten seconds. Look at the foam from the side. New shoes have a smooth midsole wall. Worn ones develop deep horizontal creases, usually starting on the outer edge of the heel or under the ball of the foot, and those creases stay visible when the shoe is sitting unloaded on a table.
Then press your thumb hard into the foam. Fresh midsole gives, then pushes back. Dead midsole feels packed down and stays dented for a moment. If you own a newer pair, press both and compare; the difference is obvious once you have felt it, and much harder to judge from memory.
Foam compresses permanently over time, and it does it long before the shoe looks scruffy. A pair that still looks presentable can be finished underneath, which is why appearance is a poor guide.
Signal two: new aches with nothing else changed
Vague, low-grade soreness in the knees or shins that arrives without any change to your training is worth taking seriously. Same routes, same weekly distance, same pace, and suddenly the front of the shins grumble for a day after every easy run. Tired midsoles are a common cause.
The important qualifier is the "nothing else changed" part. If you have added mileage, started hills, changed surfaces or come back from a break, the shoes are probably not the culprit. But if genuinely nothing is different, look at what is under your feet before you look anywhere else. Persistent or sharp pain is a physiotherapist's job, not a shopping problem.
Signal three: the outsole has worn through
Turn the shoes over. Rubber wears at the outer heel and under the ball of the foot for most people. Once it has worn through to the exposed midsole foam underneath, the shoe is done for running, and it will now wear extremely quickly because foam has no business being a ground contact surface.
Uneven wear is normal and not a fault to be corrected. Wear that has punched a hole through to the foam is a hard stop.
The upper is a separate matter. A hole in the mesh over the little toe, or a frayed heel lining, is annoying but it is not structural, and a shoe with a tired-looking upper and a healthy midsole still has running left in it. The reverse is far more common and far more of a problem: a clean, tidy upper wrapped around foam that gave up two months ago. Judge the sole, not the shoe's appearance in the hallway.
What makes a pair die faster
- Runner weight. More load compresses foam faster. Heavier runners should expect fewer miles per pair, and that is physics, not a criticism.
- Surface. Rough, stony and uneven ground works the midsole harder than smooth tarmac, and chews the outsole as well.
- Wearing them all day. Every hour standing in running shoes is compression the foam does not get back. Keep them for running.
- Heat. Drying soaked shoes on a radiator degrades the foam and the glue. Stuff them with newspaper and leave them somewhere ordinary.
- One pair for everything. Foam partially recovers with rest. Rotating two pairs gives it a day or two to do that, and both pairs last longer than they would alone.
Keeping track without becoming obsessive
Write the month you started running in them somewhere inside the tongue in biro. It takes five seconds and answers the question honestly a year later, which no memory does. If you log your runs, most apps will track shoe mileage for you and that is fine as a rough tally.
Then set a habit of checking the midsole every few weeks once the pair has some months on it. Crease, press, compare. When the foam clearly no longer springs back, order the replacement rather than waiting for it to get worse, and run the new pair in alongside the old one for a couple of weeks. That way you never end up doing a long run in a dead shoe because the new ones have not turned up.
Done that way, knowing when to replace running shoes stops being a guess about mileage and becomes a five-second check you do without thinking about it.
Old pairs are not rubbish, incidentally. They are perfectly good for the garden, dog walks and gym sessions, they just should not be doing your long run. If you are replacing rather than repeating, it is worth browsing the current running shoe range with your old pair to hand, and picking up the other bits and pieces like socks at the same time, because worn socks quietly cause blisters that get blamed on the shoes.