Objective To study the effects of daily treatment time on functional gain of patients who have had a stroke. Design A retrospective cohort study. Setting An inpatient rehabilitation hospital (IRH) in northern California. Participants Three hundred sixty patients who had a stroke and were discharged from the IRH in 2007. Interventions Average minutes of rehabilitation therapy per day, including physical therapy, occupation therapy, speech and language therapy, and total treatment. Main Outcome Measures Functional gain measured by the Functional Independence Measure, including activities of daily living, mobility, cognition, and the total of the Functional Independence Measure (FIM) scores. Results The study sample had a mean age of 64.8 years; 57.4% were men and 61.4% were white. The mean total daily therapy time was 190.3 minutes, and the mean total functional gain was 26.0. A longer daily therapeutic duration was significantly associated with total functional gain (r = .23, P = .0094). Patients who received a total therapy time of <3.0 hours per day had significantly lower total functional gain than did those treated ≥3.0 hours. No significant difference in total functional gain was found between patients treated ≥3.0 but <3.5 hours and ≥3.5 hours per day. The daily treatment time of physical therapy, occupational therapy, and speech and language therapy also was significantly associated with corresponding subscale functional gains. In addition, hemorrhagic stroke, left brain injury, earlier IRH admission, and a longer IRH stay were associated with total functional improvement. Conclusions The study demonstrated a significant relationship between daily therapeutic duration and functional gain during IRH stay and showed treatment time thresholds for optimal functional outcomes for patients in inpatient rehabilitation who had a stroke.