How do I calculate the cost basis for a stock that split multiple times and then sold some of in 2017?

[gregviets · Accepted solution]

The cost basis would use the same ratio as the number of shares sold.  For example, if you sold three-quarters of the 2017 shares then the cost basis would be 3/4 of the original cost. The number of shares before and after the splits should make no difference in determining the cost basis.