I know there are a lot of variables that influence these answers.
I’m just looking for a general ‘rule of thumb’, not a 100% accurate figure.
So, my two ‘on average’ questions are about how far do you run:
In your ‘old’ trainers before replacing them?
In your ‘new’ trainers before you considered them broken in?
Thanks,
Paul. 
PS
I know my max. distance will be reduced due to dragging extra weight around. 
my rule of thumb is always - when they get uncomfy to do a run in
I’ve never had an issue breaking in trainers. Always just run with them and they’ve felt fine.
I’ve currently got two pairs of zoom flys in rotation with well over 800kms on them and they still feel fine.
Also retired some at 500/600 as they just felt dead and started to give me hip/glute issues
Max distance is when the arch support goes.
I tend to feel this after 12km / 1 hour runs in broken shoes.
I’d guess it’s ~600km for me.
But then they’re good for bricks, 30 min easy jogs and dog walking 
Probably say 50km for “breaking in”
Just to loosen them up and get the fit right more than anything.
If I’d bought a new pair of shoes for a race, I’d wear them for all sessions during race week, so maybe even 30km ?
Most general mileage trainers i’ll get 1,000km out of, the odd pair will only reach 600km.
For trail shoes my uppers tend to disintegrate before the shoe.
Don’t really break them in at all. I tend to wear shoes that i’m pretty conifdent i’ll like, but i’d happily knock out a long run in a brand new pair of shoes. Though some will soften a tad after about 60kms for me.
As @adam and @Poet mention, i normally start getting achey legs or the beginning of a niggle. Invariably i’ll look at my shoe log and see that they’re creeping up towards that upper ceiling.
The problem i have is that most of them still look like a perfectly decent shoe. No good for me to run in, but there are only so many pairs you need for gardening or walking! I’m still gardening in my Peg 32s from about 4/5 years ago. I feel bad ‘just’ recycling them.
Worn out - for me it’s a sore side of my right Achilles that tells me they’re no longer giving me enough support
Breaking in - one run to check for obvious rub points or a change in size between different iterations of the same shoe (I’m looking at you Brooks Adrenaline c. 2015 )
or stupid design changes that ruin the whole flippin shoe (looking at you Kinvara 5 onwards!!)
Thanks all. 
It’s been years since I’ve had to track mileage in my trainers as per TT1.0 / @AndyS.
But I ran more miles in 2020 than the four years from 2015 to 2018 combined.
So, I’m not sure if I’m now feeling this extra mileage, or the trainers are past their best.
I’ve already got my new pair on the go, but with just a couple of short runs so far.
Therefore, I’ll switch over ‘early’ to be on the safe side and add to my ‘casual’ collection.
Cheers,
Paul.
I’ve got a couple with over 2000km on, they’re getting pretty ropey and beginning to get holes all the way through the soles that let in water, so will probably need to get some new ones soon
no idea what breaking in is, you just run in 'em.
This. Mine normally last around 500km. I am bigger and heavier than most. But I can tell when they are shot, they have no bounce and it becomes uncomfortable.
I tend to go to 1000km to 1200km per pair before I notice that I’m getting niggles in them compared to other shoes.
800 - 1,000 km but i tend to scuff which wears unevenly…
@Adam mentioned running two pairs at a time which is good, i tend to use 3 or 4 different types of shoes at a time…
I have never really had a problem running in new shoes but still use one or two short runs to establish how they affect my running form…
You’ve seen my soles…right?
110km
Yeah, this was what I was just about to say. Certainly sounds like Paul just has one pair of trainers he uses constantly? I have numerous on rotation. I think in the last 2-3 weeks I have used:
Peg 36
Peg 37
Zoom Fly Flyknit
Zoom Tempo NEXT%
Vaporfly 4%
Mixing it up seems to help my body, and you obviously lower the wear on a given pair of trainers at once. Although clearly you have to spend more up front to have multiple pairs!
Like others have said, I keep them until they start to feel uncomfortable. I generally have 3-4 road shoes of different types (heel to toe drop, stack height) and trail shoes. Never need to break a shoe in.
Holy smokes Batman!!!
I’ll take a photo of mine next week after I’ve done 100km in them.
That’s horrific wear!
In the past two weeks, I’ve used
Saucony Speedcross GTX
Nike Wildhorse 5
Kerra Tiger
Peg 36 Shield
Peg 37
Vaporfly 4%
Vaporfly 4% (old pair)
Next%
Not used the Zoom Fly SP or Zoom Fly FlyKnits in a while now.
Although I do think I have a problem 
Thanks again everyone.
Every day is a school day on here! 
Yes, I just have one pair of ‘active’ running shoes at a time.
But in the past, I would have ensures a ‘planned’ transition from old to new.
(Long runs in old + short runs in new >>>> long runs in new.)
As I said, it have been over a decade since I had to worry about any of this.
Even if I include my retired from running, but still wearing, trainers I can’t compete with @Poet.
Cheers, Paul.
running shoe manufacturers must love you!
The beauty of learning new skills to make props, is that I can now make “patches” for the offending areas
An auxillary benefit that I like about minimal running shoes is lack of issues regarding wear (and “breaking in”, what’s that?). There’s little possibility of uneven wear or degradation when you have basically no stack of cushioning in the first place. They weigh half or less compared to the cushioned trainers I wore 10y ago (Adidas Supernova, 320g+, 8mm drop) and last at least as long. The pic shows a range going down to the minimal blue ones. Next to the cycle overshoes are Inov8 Terraclaw which I liked for trail - 220g, 4mm drop, wide. The black-turquoise are X-Talon, not minimal but around 200g, with sufficient grip for fell terrain (Triathlon X, Hellvellyn etc). The yellow ones are another Inov8, 155g and 3mm drop, loved these and got through 3 pairs when I ran the roads mostly, up to iron distance tri. The blue ones are my current favourite and properly minimal, a Merrel vaporglove clone, sub-150g with zero drop and basically no cushion. They also have no arch; I have high arches but they don’t need supporting.
To use less or no cushion you need to reassess/rework your gait but I’d strongly recommend that for both speed and resilience (even if you end up racing in something high tech). Over the years I’ve followed Saxby (briefly), then trained with Kehoe/Borg in Dublin, Paul Tierney and now Keith Bateman.
Not the simple answer you may have been looking for, but it really does depend on the sort of shoe and gait.
