Analysis of 2,036 UK women tracked over three decades reveals perimenopause carries 19% higher odds of depression compared to reproductive years, while postmenopause shows no elevated risk. Women experienced gradual increases in depressive symptoms with both reproductive and chronological aging, but contrary to common assumptions, the study found little evidence of marked symptom spikes during menopause stages themselves. This challenges prevailing narratives about menopause as a period of sustained mental health decline. The finding suggests perimenopause represents a discrete vulnerability window rather than the beginning of long-term psychological deterioration. For women's health, this indicates targeted interventions during the perimenopausal transition—when hormone fluctuations are most erratic—could prevent depression without necessitating lifelong management strategies. The research also disentangles reproductive aging effects from normal chronological aging, a methodological advance in menopause research. However, this preprint awaits peer review, and results may change. The study's strength lies in its exceptional 30-year follow-up period, though findings from this UK cohort may not generalize globally. This appears confirmatory rather than paradigm-shifting, refining our understanding of depression timing during reproductive transitions.