This study investigates the causal relationship between paid working hours, perceived health, and wages in South Korea, with a focus on gender disparities. We hypothesize a U-inverted relationship between paid working hours and health, where health improves with longer hours up to a point and then declines. We further hypothesize a reciprocal positive relationship between health and wages, and that women face negative health impacts at lower work-hour thresholds than men. Using 13 years of data from the Korean Labor and Income Panel Study (KLIPS) from 2009 to 2021, we apply cross-lagged panel analysis and instrumental variable estimation. Results show an inverted U-curve relationship, with health inflection points at 41.36 h for men and 28.95 h for women, and a positive bidirectional link between health and wages. The inflection point for women suggests they experience negative health effects sooner than men, likely due to unpaid domestic work. This study provides causal evidence on how paid working hours affect health and wages, emphasizing the need for gender-specific considerations in policy and workplace practices.