Computing accurately and effectively the impact of clock skew on statistical slack in the presence of statistically variable timing quantities that accounts for both common path credit in the common portion of the clock tree, and RSS credit in the non-common of the clock tree. The clock skew is measured on a per launch and capture path-pair basis as a function of on the post-CPPR path-specific slack (including RSS credit), total mean value of latch-to-latch delay, RSS value of random latch-to-latch delay, test guard time and test adjust. The method includes: performing an initial block-based SSTA including CPPR analysis; selecting at least one launch and capture path-pair for skew analysis; for the at least one path pair, recording post CPPR slack, total mean value of latch-to-latch delay, RSS value of latch to latch delay, test guard time and test adjust; and quantifying the impact of clock skew on statistical slack thereof.