Incremental development is the process of writing a small snippet of code and testing it before moving on. For students in introductory programming courses, the value of incremental development is especially higher as they may suffer from more syntax errors, lack the proficiency to address complicated bugs, and may be more prone to frustration when struggling to correct code. However, to evaluate the effectiveness of interventions that aim to teach programming processes such as incremental development, we need to develop measures to assess such processes. In this paper, we present a way to measure incremental development. By qualitatively analyzing 15 student coding interviews, we identified common behaviors in the programming process that relate to incremental development. We then leveraged a dataset of over 1000 development sessions – about 52,000 code snapshots at compilation time – to automatically detect the common behaviors identified in our qualitative analysis. Finally, we crafted a formal metric, called the ``Measure of Incremental Development’’ (MID), to quantify how effectively a student used incremental development during a programming session. The MID detects common non-incremental development patterns such as excessive debugging after large additions of code to automatically assess a sequence of snapshots. The MID aligns with human evaluations of incrementality with over 80% accuracy. Our metric enables new research directions and interventions focused on improving students’ development practices.