Any thoughts on what it might be?

It seems that zero commissions should completely change our stop strategies. You can have much tighter stops without any fear of your money being eaten up by commissions. On the other hand you still need some space for your trades to work. Or your loses can still out balance your winners

I would think there would be some mathematical model for optimal stop strategies when there are zero commissions. But I have not figured it out.

Any thoughts on what it might be?

I have not found any 0 cost of a trade with futures contracts yet . equities yes . It is likely the spread between the bid and ask combined with subpar order execution will cause some ugly slippage from time to time . if you use limit orders or swing trade its a good deal . if you are in and out of the market 10 times a day using market orders you may get some very bad fills . they are selling your order flow to market makers so they can front run the retail orders. it is not free trading like it appears .

Well, zero commissions are entirely a stock market thing, so as a pure futures trader I won't see it. But it is a fact of trading life for many stock traders (I believe at some brokers only). They are possible for the broker because brokers get "payment for order flow" from large firms that then take the other side of your order. Basically, the brokers have to make some money to make up for the lost commissions, and they do. The firms that pay for the order flow have to make money to make it worth their while to pay for it, and they do. The traders, one way or another, have to pay the money that the other players receive, and they do, in the form of poorer fills. It doesn't come from anyone else. And the other guys do get paid, or they wouldn't be in the zero-commission or order-flow-buying business.

I don't trade stocks any more, but if I did, I would just shrug and say "Another cost of doing business." But there is a cost, since no one does anything for nothing, and specifically no one gives up a revenue source (commissions) for nothing.

That being said, I have no idea how to answer or even to think about the original question, which was whether and how zero stock commissions should change your stop strategy. I do think that the idea that "You can have much tighter stops without any fear of your money being eaten up by commissions" leaves out the fact that part of your money will now go toward having less favorable fills, or at least it may. That is what the firms who pay for order flow expect to happen, at least, as they get the benefit of taking your order on their terms. I think we can say that they have certainly developed a mathematical model for that, which is why they are paying for your order in the first place.

If it were me, I would place my stops according to what the market is doing, as I always do, and just shrug about the fact that I am paying to trade through a different avenue now: how my orders are filled instead of through commissions.

Just my thoughts.

Bob.

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Edit: Proving that there's always another way to look at something, this article on Wikipedia mentions another view, that payment for order flow can improve customer fills, and it also gives space to the contrary view that it costs or can cost the customer.

https://en.wikipedia.org/wiki/Payment_for_order_flow

To me, it still comes down to somehow the brokers and the market-makers make more this way than they would without it, but maybe in some situations the customer makes out too and it is better for everyone. And maybe there is a Santa Claus . But you can decide.