What determines deal price on stock exchange?

Question

Let's say I'm interested in buying some shares, and I place an order to buy at 80c. At the same time, someone is willing to sell his shares at 40c.

Now I'm told by the bank that they have a best execution policy: i.e. if I want to buy at 80c but it can be bought at a lower price, then the actual price may be lower than what I specified. However, the seller's bank most likely has a similar execution policy.

With that reasoning, although a match is made and the deal may be done, it may be executed at any price between 40c and 80c. How does the stock exchange determine which price to use?

Answer 1

Stock prices are set by bidding. In principle, a seller will say, "I want $80." If he can't find anyone willing to buy at that price, he'll either decide not to sell after all, or he'll lower his price. Likewise, a buyer will say, "I'll pay $70." If he can't find anyone willing to pay that price, he'll either decide not to buy or he'll increase his price. For most stocks there are many buyers and many sellers all the time, so there's a constant interplay.

The typical small investor has VERY little control of the price. You say, "I want to buy 10 shares of XYZ Corporation and my maximum price is $20." If the current trending price is below $20, your broker will buy it for you. If not, he won't. You normally have some time limit on the order, so if the price falls within your range within that time period, your broker will buy. That is, your choice is basically to buy or not buy, or sell or not sell, at the current price. You have little opportunity to really negotiate a better price. If you have a significant percentage of a company's total stock, different story.

In real life, most stocks are being traded constantly, so buyers and sellers both have a pretty good idea of the current price. If the last sale was ten minutes ago for $20, it's unlikely anyone's going to now bid $100. They're going to bid $20.50 or $19.25 or some such. If the last sale was for $20 and your broker really came to the floor and offered to buy for $100, I suppose someone would sell to him very quickly before he realized what an outrageous price this was.

I use TD Ameritrade, and on their web site, if I give a price limit on a buy that's more than a small percentage above the last sale, they reject it as an error. I forget the exact number but they won't even accept a bid of $80 if the stock is going for $40. They might accept $41 or $42, something like that.

Answer 2

Price is decided by what shares are offered at what prices and who blinks first.

The buyer and seller are both trying to find the best offer, for their definition of best, within the constraints then have set on their bid or ask. The seller will sell to the highest bid they can get that they consider acceptable. The buyer will buy from the lowest offer they can get that they consider acceptable. The price -- and whether a sale/purchase happens at all -- depends on what other trades are still available and how long you're willing to wait for one you're happy with, and may be different on one share than another "at the same time" if the purchase couldn't be completed with the single best offer and had to buy from multiple offers.

This may have been easier to understand in the days of open outcry pit trading, when you could see just how chaotic the process is... but it all boils down to a high-speed version of seeking the best deal in an old-fashioned marketplace where no prices are fixed and every sale requires (or at least offers the opportunity for) negotiation.

"Fred sells it five cents cheaper!" "Then why aren't you buying from him?" "He's out of stock." "Well, when I don't have any, my price is ten cents cheaper." "Maybe I won't buy today, or I'll buy elsewhere. "Maybe I won't sell today. Or maybe someone else will pay my price. Sam looks interested..." "Ok, ok. I can offer two cents more." "Three. Sam looks really interested." "Two and a half, and throw in an apple for Susie." "Done."

And the next buyer or seller starts the whole process over again. Open outcry really is just a way of trying to shop around very, very, very fast, and electronic reconciliation speeds it up even more, but it's conceptually the same process -- either seller gets what they're asking, or they adjust and/or the buyer adjusts until they meet, or everyone agrees that there's no agreement and goes home.