Purpose The negative consequences of job insecurity on the well-being of individuals are well known. However, the perceptions of job insecurity over time and how some factors such as social support may affect them have received limited attention. This study follows precarious schoolteachers for three weeks before the end of their contract to explore how their perceptions of job insecurity evolve over time. Design/methodology/approach The participants were 47 precarious schoolteachers who first completed a general questionnaire, then a diary survey on nine occasions over the course of the three weeks. Data was analysed with MPLUS 7.3. Findings The results suggest intra-individual differences regarding the way job insecurity was perceived over time. An additional discovery was that support provided by the school principal was negatively related to changes in job insecurity over time. Research limitations/implications The relatively small sample size, which includes only precarious schoolteachers, and the methodology complexity of the diary are limitations of this study. Practical implications This study highlights the subjective nature of the perceptions of job insecurity. It also shows the importance of the school principal's social support towards precarious schoolteachers; therefore, practitioners should propose interventions to enhance the quality of principal–teachers relationships. Originality/value This study contributes to the literature by investigating how perceptions of job insecurity evolve over time and the role of social support.