A static timing analysis method and apparatus that determine an expected design condition surrounding a target cell in an integrated circuit design. A derate adjustment is determined based on the expected design condition for a target cell and a timing derate, representing variation in propagation delay for a default design condition, is then adjusted based on the derate adjustment. An expected timing of a signal path including the target cell is determined based on the adjusted timing derate. The derate adjustment may be determined based on simulated variance of the propagation delay through the target cell for the expected design condition. This approach avoids unnecessary optimism or pessimism in the timing derate, which reduces the number of false positive or false negative detections of timing violations in the static timing analysis.