Granularity of limit order

@David and team - I wonder why T212 restricts the granularity of the the price that can be entered for a limit order. For example, looking at SWDA just now, I can enter a buy order only at a full number of pence, such as 5023p or 5024p. With other brokers I could, if I wished, be able to enter, 5023.5 or 5023.75. Looking at the recent trade history on the LSE, I can see that trades were made at prices of 5022.86p, 5,022.79p. I might like to set my limit order at a price close to one that has recently traded. Do you make a restriction for some reason? Similarly, for ISF, I can enter only 734.40 or 734.50, not 734.45. If I try to enter 734.45 the system rounds it down to 734.40. The most recent trade was at 734.57. Other brokers would allow me to enter at limit order at 734.45 if I wished.

I also wonder if “fill prices” are rounded. I wonder if when trading with T212 I would see a market order filled at 5023, when with another broker it might be filled at 5022.86.

I appreciate that the restriction/rounding will only be meaningful when one trades in 5 figure sums of money. Nonetheless, I am curious.

Thinking further on this, perhaps I (and other T212 customers) would appreciate a small education on how market order books actually work. When I see a record that someone bought 2617 shares of ISF at 734.38p (as happened today at 12:57), perhaps this means the person made a market order and it was partly filled at 734.30 and partly at 734.40. Perhaps it is actually impossible for a limit order to be placed at 734.38. The “tick size” for ISF is 0.1 and so all order book prices are multiples of that. I expect this is all highly regulated and so T212 does nothing materially different to other brokers. But other brokers do accept limit orders at prices that have smaller granularity than the tick size. So I remain curious.

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@Richard.W LSE does list the trades you just mentioned but they’re off-book trades (market makers). They’re not trades executed directly on London Stock Exchange’s books. Notice how all SWDA “Automatic Trade” trades are exactly .00 while “Off-book” are .XX.

In essence, trades sent & executed directly on LSE can’t always have high precision. However, If your broker isn’t sending the trade to LSE but internalizing it, the precision can be anything they want it to.


@David How interesting. Thanks for the info. I can now understand the reason for the granularity of T212 limit order prices.