For options, the estimated price is calculated using the Ask amount (see Bid/Ask) multiplied by the number of contracts you are purchasing multiplied by 100 (since there are 100 shares per contract).
For stocks, the estimated price is calculated using the Ask amount (see Bid/Ask) multiplied by the number of shares you are purchasing.
We use estimated prices because the actual execution price can differ from the real time pricing in the app due to market conditions at the point of transaction.