Background <p>Limb length discrepancy (LLD) following total knee arthroplasty (TKA) may affect functional outcomes and patient satisfaction. However, relative impact of coronal and sagittal plane deformity correction on change in limb length (CLL) following TKA are still not fully understood. The aim of this study is to guide the surgeon regarding the expected change in limb lengths following correction of coronal and sagittal plane deformities.</p> Methods <p>This retrospective study comprised 237 primary TKAs conducted by a single surgeon from August 2024 to July 2025. Preoperative deformities consisted of 215 varus and 22 valgus knees. Standing anteroposterior radiographs of full length were used to assess the hip–knee–ankle (HKA) angle and limb length before and after the operation. Flexion contracture was assessed through clinical measurement. Correlation and multivariable regression analyses were conducted to ascertain predictors of limb length alteration, while adjusting for possible confounders such as patient height and polyethylene insert thickness. A regression-based predictive model was subsequently developed.</p> Results <p>Mean limb length showed a notable increase after TKA (10.4 ± 9.1&#xa0;mm; <i>p</i> &lt; 0.0001). The preoperative HKA angle showed a significant positive correlation with CLL in both varus and valgus knees and remained the strongest independent predictor (<i>p</i> &lt; 0.001 for varus; <i>p</i> = 0.046 for valgus). Preoperative flexion contracture did not show a significant independent association with CLL. Patient height and the thickness of the polyethylene insert did not have a notable effect on changes in limb length.</p> Conclusions <p>TKA leads to consistent limb lengthening, mainly caused by the correction of coronal plane deformities. Estimating limb length changes before surgery can aid in surgical planning and patient counseling, especially in cases of unilateral or staged bilateral TKA.</p> <p><i>Level of evidence</i> III, Retrospective comparative cohort study</p>