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BACKGROUND: In randomized trials, early improvement with biologic therapy in Crohn's disease (CD) and ulcerative colitis (UC) is linked to better long-term outcomes. However, some patients may respond later (late remitters). The frequency of such late remitters, predictors of who may belong to this group, and the long-term outcome of such patients has not been examined robustly.METHODS: This prospective single-center study enrolled patients with moderate-to-severe CD or UC initiating biologic or small molecule therapy. Disease activity was assessed prospectively using Harvey Bradshaw Index (CD) and Simple Clinical Colitis Activity Index (UC). Patients were followed for one year. Early remitters achieved clinical remission (HBI≤4, SCCAI≤2) by week 14. Late remitters did not achieve remission by week 14 but attained remission by week 30. Non-remitters failed to achieve remission by week 30.RESULTS: Our cohort included 596 patients (280 CD, 316 UC) initiating anti-TNF (n=174), vedolizumab (n=171), anti-IL (primarily ustekinumab, n=116), or JAK inhibitors (primarily tofacitinib, n=135). Most (89%) had prior biologic exposure. Clinical remission at week 14 occurred in 37%; an additional 14% achieved remission between weeks 14 and 30 (late remitters). Late remitters had slightly shorter disease duration but comparable demographics and disease characteristics to early responders. Late remitters had similar rates of clinical (64% vs. 63%) and endoscopic remission (43% vs. 49%) at week 52 compared to early remitters, with superior outcomes compared to non-remitters (13% and 16%, respectively; p<0.001).CONCLUSIONS: About one-sixth of patients achieved delayed remission by week 30. They had comparable one-year outcomes as early remitters. Identifying predictors of delayed remission could help prevent early therapy discontinuation without affecting long-term outcomes.