Aims: Career counselling is a complex process. Traditional career counselling is unidirectional in approach and ignores the impact and interactions of other factors. The Systems Theory Framework (STF) is an emerging framework that illustrates the dynamic and complex nature of career development. Our study aims to i) explore factors affecting senior residency (SR) subspecialty choices, and ii) determine the suitable utility of the STF in career counselling. Methods: A prospective observational cohort study of internal medicine residents was done. Surveys were collected at three time points. The Specialty Indecision Scale (SIS) assesses the individual components and expert consensus group derived the questions for the contextual components. We measured burnout using the Mashlach Burnout Inventory. Process influences were assessed via thematic analysis of open-ended question at the 3 rd survey. Results: 82 responses were collected. There was a trend towards older residents being ready to commit albeit not statistically significant. At year 1, overseas graduands (OR = 6.87, p= 0.02), lifestyle factors (t(29)=2.31, p=0.03, d= 0.91), individual factors of readiness (t(29) = -2.74, p=0.01, d= 1.08), indecisiveness (t(27)= -0.57, p=0.02, d= 0.99) and self-doubt (t(29)= -4.02, p=0.00, d= 1.54) predicted the resident's ability to commit to SR. These factors change and being married (OR 4.49, p= 0.03) was the only factor by the 3 rd survey. Male residents are more resolute in their choice (OR= 5.17, p= 0.02). Conclusion: The resident's choice of SR changes over time. The STF helps in understanding decision-making about subspecialty choices. Potential applications include: i) initiation of career counselling at year 1 and ii) reviewing unpopular SR subspecialties to increase their attractiveness. Keywords:Internal Medicine Residents, Career Counselling, Senior Residency Practice Highlights  Career decision-making is a complex process and there is a need for a holistic approach to it.  The Systems Theory Framework consists of a multifaceted range of content (individual and contextual factors) and process influences (change over time, recursiveness, chance) to illustrate the dynamic and complex nature of career development.  The resident's choice of senior residency changes over time throughout their residency. The factors that affect their subspecialty choice transit from individual factor of indecisiveness, self-doubt and readiness in year 1 to contextual factor of lifestyle by year 3.  Male residents are more resolute in their choice of senior residency.  Reasons for resident's change of choice of senior residency include i) experience during rotation ii) lifestyle choices and iii) influences from peers and seniors.