Hello, Suppose selling a stock has a $5 transaction fee ($5 buy, $5 sell). Do you marry each transaction cost to the security buy/sell? Or do you simply add up all the transaction fees you incurred for that quarter and deduct them from any capital gains that quarter? For example, supposed you bought a stock for $1000, and it had a $5 fee to buy the stock. Then you sold it for $1100, but also had a $5 selling fee. So it would look like this: ($1100 -$5) - ($1000 + $5) = $1195 - $1005 = $90 capital gain. The other style would be something this: $1100 - $1000 = $100 capital gain $30 trading fees for the month (however they happened to arrive). So you have $100 - $30 = $70 capital gains after fees.
You include the commissions in your buy and sell transactions. So the proceeds would be $1100 - $5 = $1095 and the cost basis would be $1000 + $5 = $1005 for a total gain of $90. https://turbotax.intuit.com/tax-tips/rental-property/cost-basis-tracking-your-tax-basis/L4i1f9qB1
Many brokerage firms, if not all of them, add and subtract commission fees from the buy and sell orders automatically. Therefore, you do not have to add or subtract anything. Just down load your trades to TurboTax or whatever tax software you use and you are done.