No study has compared minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) to lateral lumbar interbody fusion (LLIF) in time to achieve the minimum clinically important difference (MCID) and factors associated with delayed MCID achievement. To compare time to achieve MCID between MIS-TLIF and LLIF and to evaluate the factors associated with delayed time to achieve MCID for the patient-reported outcome measures (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. Patients undergoing MIS-TLIF or LLIF with preoperative PROMIS-PF, ODI, VAS back, and VAS leg were retrospectively reviewed through a single-surgeon database. Two-hundred and twenty-five patients were identified, with 153 patients undergoing MIS-TLIF and 72 patients undergoing LLIF. Patient-Reported Outcomes Measurement Information System Physical Function (PROMIS-PF), Oswestry Disability Index (ODI), Visual Analog Scale (VAS) back, and VAS leg. Patients undergoing MIS-TLIF or LLIF with preoperative PROMIS-PF, ODI, VAS back, and VAS leg were retrospectively reviewed through a single-surgeon database. PROMs were collected at preoperative and 6-week, 12-week, 6-month, 1-year, and 2-year postoperative time points. MCID achievement was determined through comparison of change in PROMs to established values in literature. Kaplan-Meier survival analysis was utilized to determine time to achieve MCID. Predictive values of delayed MCID achievement were determined through multivariable Cox regression analysis. Two-hundred and twenty-five patients were identified, with 153 patients undergoing MIS-TLIF and 72 patients undergoing LLIF. Overall MCID achievement rates for MIS-TLIF patients were 74.1% for PROMIS-PF, 67.5% for ODI, 71.8% for VAS back, and 65.8% for VAS leg, while MCID achievement rates for LLIF patients were 74.7% for PROMIS-PF, 62.8% for ODI, 71.7% for VAS back, and 69.7% for VAS leg. The mean time to achieve MCID in weeks for MIS-TLIF patients was 24.51±38.41 for PROMIS-PF, 32.10±35.43 for ODI, 32.52±35.37 for VAS back, and 30.28±33.42 VAS leg, while mean time for LLIF patients were 21.03±30.01 for PROMIS-PF, 22.68±29.59 for ODI, 26.91±30.49 for VAS back, and 27.34±29.29 for VAS leg. Surgical procedure was only significant in Kaplan-Meier survival analysis for PROMIS-PF, where LLIF patients achieved MCID significantly earlier (p = 0.011). Multivariable Cox regression demonstrated early predictors of MCID achievement for elevated preoperative VAS back, VAS leg, and ODI scores, diagnosis of hypertension, and diagnosis of herniated disc (HR 1.03-2.82). Late predictors of MCID achievement were diagnosis of diabetes, Hispanic ethnicity, workers’ compensation, and increased preoperative PROMIS-PF (HR 0.33-0.95). Independent of surgical procedure, most patients achieved MCID within 1-year of surgery. Patients undergoing LLIF achieved MCID earlier in physical function compared to patients undergoing MIS-TLIF. Significant factors for early MCID achievement were elevated baseline disability and pain scores, diagnosis of hypertension, and diagnosis of herniated disc. Significant factors for late MCID achievement were diagnosis of diabetes, Hispanic ethnicity, workers’ compensation, and elevated baseline physical function. These factors may be useful in managing postoperative expectations for patients. This abstract does not discuss or include any applicable devices or drugs.