There is a gap in the literature comparing time to minimum clinically important difference (MCID) achievement and factors associated with delayed MCID achievement for patient-reported outcome measures (PROMs) between the minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) and anterior lumbar interbody fusion (ALIF). To compare time to MCID achievement and factors associated with delayed MCID achievement the PROMs of Patient-Reported Outcomes Measurement Information System Physical Function (PROMIS-PF), Oswestry Disability Index (ODI), Visual Analog Scale (VAS) back, and VAS leg. Retrospective review. Three-hundred and fourteen patients were identified, with 224 patients undergoing MIS-TLIF and 90 patients undergoing ALIF. Patient-Reported Outcomes Measurement Information System Physical Function (PROMIS-PF), Oswestry Disability Index (ODI), Visual Analog Scale (VAS) back, and VAS leg. PROMs of patients undergoing MIS-TLIF or ALIF were collected at preoperative and postoperative 6-week, 12-week, 6-month, 1-year, and 2-year postoperative time points. MCID achievement was calculated through comparison of change in PROMs to previously determined values. Time to MCID achievement was compared through Kaplan-Meier survival analysis. Predictors of delayed time to MCID achievement were determined through multivariable Cox regression. Three-hundred and fourteen patients were identified, with 224 patients undergoing MIS-TLIF and 90 patients undergoing ALIF. MCID achievement rates were higher in MIS-TLIF patients for ODI (68.8% vs 53.3%, p=0.010) and VAS leg (71.4% vs 51.1%, p=0.001), while MCID achievement rates were not significant for PROMIS-PF (74.1% vs 68.9%) and VAS back (80.4% vs 74.4%). In patients who achieved MCID, the mean postoperative time to achieve MCID in weeks was 61.28±37.88 for PROMIS-PF, 49.60±34.45 for ODI, 47.42±36.65 for VAS back, and 44.02±34.07 for VAS leg in MIS-TLIF patients, while the time to MCID achievement was 51.81±35.88 for PROMIS-PF, 41.25±29.57 for ODI, 32.90±29.34 for VAS back, and 32.14±27.11 for VAS leg in ALIF patients. Accounting for patients who failed to achieve MCID, Kaplan-Meier survival analysis revealed significantly faster MCID achievement times in ODI and VAS leg for MIS-TLIF patients (p≤0.026, both). Multivariable Cox regression revealed early predictors of MCID achievement of elevated baseline PROMs of VAS back and VAS leg and diagnosis of degenerative disc disease (HR 1.03-1.54) and late predictors of ALIF procedure, Hispanic and Asian ethnicity, workers’ compensation, elevated baseline PROMIS-PF, and diagnosis of isthmic spondylolisthesis (HR 0.27-0.95). Elevated baseline ODI was an early and late predictor for PROMIS-PF (HR 0.98) and ODI, respectively (HR 1.03). Independent of surgical procedure, most patients achieved MCID within 2 years of surgery. Patients undergoing ALIF achieved MCID later in disability and leg pain compared to patients undergoing MIS-TLIF. Significant factors for early MCID achievement were elevated baseline pain scores and diagnosis of degenerative disc disease. Significant factors for late MCID achievement were patients undergoing ALIF, elevated baseline physical function, Hispanic or Asian ethnicity, workers’ compensation, and diagnosis of isthmic spondylolisthesis. Elevated baseline disability was an early and late MCID predictor for physical function and disability, respectively. Surgeons may utilize this information to convey expectations to patients. This abstract does not discuss or include any applicable devices or drugs.