Software development is often affected by user/system requirements changes. To implement requirements changes, a system which is being developed needs to be reworked. However, the term ?Rework? has not been clearly defined in the literature. Depending on the complexity of the changes, the amount of rework required varies from some software module modifications to a non-trivial alteration to the software design of a system. The effort associated with such a rework obviously will vary too. To date, there has been scant research on rework assessment, and the relationship between it and change effort estimation is hardly understood. In this paper, we present a definition for rework, and describe a method of assessing rework for implementing software requirements changes. Our method consists of three stages: namely (i) change identification; (ii) change analysis; and (iii) rework assessment. To demonstrate the practicality that it enables developers to compare the rework between the different options available for implementing a requirements change and to identify the one which is less invasive and requires lesser amount of modifications to the software system design, we explain our concept with the use of a running example.