Select the most advantageous cost basis method
Finally, take a look at how the cost basis on your investments is calculated. Cost basis is simply the price you paid for a security, plus any brokerage costs or commissions.
If you have acquired multiple lots of the same security over time, either through new purchases or dividend reinvestments, your cost basis can be calculated either as a per-share average of all the purchases (the average-cost method) or by keeping track of the actual-cost of each lot of shares (the actual cost method).
For tax-loss harvesting, the actual-cost method has the advantage of enabling you to designate specific, higher-cost shares to sell, thus increasing the amount of the realized loss.