How to calculate Defect Leakage ?

Defect Leakage metric is the ratio of Number of defects attributed to a stage but only captured in subsequent stages to the sum of Total number of defects captured in that stage and Total Number of defects attributed to a stage but only captured in subsequent stages. It is used to determine the % of defect leaked to subsequent stages. Lower the value to Defect Leakage better is the quality of testing.

Defect Leakage is calculated at overall project or stage level or both. It is measured in percentage (%).

How to calculate the Defect Leakage:

Defect Leakage=(Number of defects attributed to a SIT but captured in UAT) / (Total number of defects captured SIT + Total Number of defects attributed to SIT but captured in UAT)

Example:

Total number of defects captured in SIT	Number of defects attributed SIT but captured in UAT	Defect Leakage
72	8	10

Defect Leakage= 8 / (72+8) * 100

                           = 10 %

Note: In above example the current stage is considered as SIT (System Integration Testing) and subsequent stage is considered as UAT (User Acceptance Testing). The user needs to understand the current and subsequent stage and accordingly need to modify the formula.