Line 101 (contract sales price) is the basis of the property.
This is the starting point. From there you add certain settlement fees paid when you bought the home and the cost of any improvements made to the home.
For more information, see the following IRS articles:
NOTE: If you lived in and owned the home for at least two out of the last five years, you do not have to report the sale if your gains are less then the exclusion amounts of $250,000 if filing Single or $500,000 if filing Married Filing Jointly (and both lived in and owned the home for two years).
