Objective To evaluate the impact of functional bladder capacity (FBC) on clinical outcomes after a staged neuromodulation procedure. Materials and Methods Adults in our prospective neuromodulation database were evaluated. Data were collected from medical records, voiding diaries (FBC defined as average volume per void), Interstitial Cystitis Symptom Index-Problem Index, Overactive Bladder Questionnaire, and Global Response Assessment over 3 months. Descriptive statistics, Pearson's chi-square tests, Wilcoxon rank sum tests, logistic regression, repeated measures analyses, and Spearman correlation coefficients were performed. Results Of the 216 patients (mean age 59 years; 84% female), most had urinary urgency and frequency with or without urge incontinence (71%), a sacral lead placement (82%), and implantable pulse generator (IPG) implantation (92%). Baseline FBC was similar between implanted and not implanted patients (P =.17); however implanted patients had a median 19 mL increase in FBC after lead placement compared to a 2.7 mL decrease in explanted patients (P =.0014). There was a strong association between percent change in FBC after lead placement and IPG implantation (P =.021; C-statistic 0.68), but baseline FBC (mL) was not associated. Baseline FBC (mL), or percent change in FBC after lead placement, was not related to symptom improvement. When grouped by baseline FBC < 150 mL and FBC ≥ 150 mL, FBC only improved significantly in the <150 group but both demonstrated significant improvements in symptoms. Conclusion FBC improvements were associated with IPG implantation but not other symptom measures. Patients with low FBC (baseline FBC < 150) also achieved significant improvements in symptoms.