This is a question I get asked quite a lot and my answer isn't always appreciated...
That's because it's one of those "how long is a piece of string?" type of questions.
My answer is generally along the lines of: "It's difficult to give a simple one-size-fits-all type answer, as there are so many variables to consider."
In my opinion the manufacturer's general 'guidelines' aren't too far off but for some shoes they can be a little bit conservative. I've owned shoes that have lasted for 650 - 700 miles. I might be being cynical - but shoe makers do have a vested interest in getting you to buy more shoes and therefore improve their profit margins.
Money grabbing multi-national corporations aside, there are some basic ground rules to think about when deciding whether or not to change your shoes.
What should you consider when deciding if it's time to replace your favourite running shoes?
Type of Shoe
The surface that you will be running on: I touched on this briefly above. Generally the harder, more dense and abrasive a running surface is, the quicker it will wear out the grip/soles of your running shoes.
The heavier you are, the more punishment your shoes will take and potentially this will lead to them wearing out quicker for you than for another runner that is much lighter than you. Maybe this could be another incentive for you to loose a few excess pounds. If the thought of dragging any dead-weight around for an entire race (especially a marathon or ultra) isn't incentive enough.
Or perhaps you have a waif-like, athletic running physique like me. In which case congratulations your running shoes should last really well. But if you want to buy more, then you know what to do - donuts and ice-cream for breakfast...
The cushioning material, which is usually a rubber or foam material can become compacted and stiffen up compared to when it was fresh out of the box. Again, the heavier you are the quicker this will occur.
Some shoes - especially Nike models also use 'air' for their cushioning. It is possible that these air-bags (or whatever the correct term is) can become damaged. I had this happen to me when I trod on a thorny twig on a trail run. A puncture like this can lead to the air cushioning being less effective - just like when the foam cushioning becomes compacted.
If/when this happens you'll start to feel it on your runs and will potentially feel a bit more sore afterwards or your joints (especially knees) may start to grumble a bit when you run. That’s a sign that it’s time to go shoe shopping.
Most runners are heel strikers and as such this normally means that the heel - in particular the outside edge of the heel will wear out first. This is also generally the thickest most cushioned part of most shoes and may well have a thicker tread too.
But if you have a mid-foot or forefoot foot strike, this could mean that the shoe will wear differently and perhaps wear out more quickly depending on whether the shoe has been designed specifically for your foot-strike pattern. Quite a few 'minimalist' type shoes are aimed at people that have a mid-foot to moderate forefoot strike pattern. So won't necessarily wear as well for heavy heel strikers.
I don't mean how loud your footsteps are - though if you have an inefficient foot slapping running technique it won't do you any favours on a number of levels - not just how long your shoes last.
How often and how far you will be running will obviously be a factor in how quickly your shoes wear out. I'm not necessarily thinking about total miles here. But purely time spent in your shoes. Obviously if you only run an average of 15 miles a week, your shoes will last you ten times longer than if you were running 150 miles a week. Likewise if you don't just wear your shoes to run in and you wear them for other activities - like going to the gym, gardening or climbing Jack's magic beanstalk - all of those other activities will be reducing the overall life expectancy of your shoes as well.
Materials used - especially for the soles/grip and cushioning can differ between manufacturers and indeed different models of shoe by the same manufacturer could use different materials too. Each individual type of rubber compound for the grip and/or foam for the cushioning will wear out differently. Some are just more durable than others.
The entry level/cheaper models of most brands tend to use less durable materials and in my experience don't last as long as the more expensive models. So buying bottom of the range shoes could prove to be a false economy. That doesn't necessarily mean that buying the top-end shoes is best though. Wherever you buy your shoes, it's worth shopping around for bargains/sales.
How you look after your shoes can also be a significant factor in how long they last. Making sure they dry well after getting them wet and cleaning off excess mud will help ensure the uppers last reasonably well. Leaving them soaking and covered in mud can accelerate the degradation/rot of the uppers.
I don't recommend that you put your shoes in a washing machine ever (though I know plenty of people that do) and definitely not in a tumble dryer. Doing this can affect the glues/adhesives used to stick different bits together and can result in your shoes literally falling apart.
Do keep your shoes clean, brush off any mud/dirt once dried
Don't put your shoes in a washing machine or tumble dryer
My advice is that you inspect your shoes regularly and check their general condition and also for specific wear. If they look like they're starting to fail in any way. Replace them.
A general rule of thumb that I use is to have a good look at the tread and if any part of it has worn away completely so that the cushioning material below is exposed - it's time to retire those shoes and get new treads on.
Smooth treads = lack of grip, which can be dangerous - leave you more susceptible to slips/trips/falls/injury in wet conditions.
Having more than one pair of shoes, so you can use them in rotation will make shoes last longer and also gives your body a bit of variety. As different shoes and indeed different running surfaces will impact on your running gait and variety is good.
Get to grips with the peculiarities of your running shoes, check them for wear regularly. If they start to show signs of excessive wear, or you feel that the grip or cushioning are a little sub-par. Then it's time to go shopping for a replacement pair.
If you also heed my advice and have more than one pair of running shoes on the go at all times in rotation. You won't be without a pair of shoes and your running won't suffer/have to stop before you get a new pair.
I also like to shop around in the online sales and keep a pair on stand-by, ready for when one of my current in-use pairs is ready for retirement. That way there is absolutely no down-time involved.
But you do need a bit of room for at least 3 pairs of running shoes (more like 6 or 7+ in my case!).