Nearly two decades into the "completion agenda" in higher education, many community colleges have adopted collegewide reforms designed to improve stubbornly flat rates of student success and address persistent equity gaps. The longer-term effects of such collegewide reforms may take years to observe. In the meantime, college leaders need to know whether changes they make in the short run are associated with longer-term student success. Measuring the progress and effects of institutional reform is particularly vital in economically important STEM fields. Drawing on administrative records from transfer-intending community college starters across three states, this study develops and explores potential indicators of early STEM program momentum. We find that a relatively simple set of STEM momentum metrics--notably early completion of calculus or non-math STE coursework specified in statewide STEM transfer pathways and, to a lesser degree, the prerequisites to such courses--are reliable indicators of subsequent STEM transfer and bachelor's degree attainment. Our findings provide support for the use of the STEM momentum metrics to formatively evaluate reforms aimed at strengthening STEM transfer outcomes and closing equity gaps in STEM bachelor's degree attainment.