I received an execution in my Paper Trader account that did not correspond to the market at the time, what happened?


A paper trading account is a simulated account trading in a simulated market.  IBKR programmatically simulates, to the best possible abilities, actual market conditions.  However, it is not a real market and prices cannot exactly match.  IBKR is simulating not only the trader’s functionality and the market, but also the role of the exchange.  In a real, live account, the order would be sent to the exchange, and the exchange would be doing the execution—not IBKR.  The exchange has an anonymous book and orders are matched anonymously.  With the simulated account IBKR is trying to simulate the role that in the real markets is played by the exchange.  While these fills may or may not be within the bounds of the live market at the time, in no way is it indicative of what would happen in the real market.  Again, IBKR is simulating the exchange’s role in the live market, and in that market the onus for order matching/filling is on the exchange.


The simulated trader is for clients to acclimate themselves to the software, test various orders and strategies, and to serve other learning functions.  There is no way to exactly replicate live markets.  They are simply too dynamic.  The IBKR simulator does a very good job of it, but no simulator could be perfect.