OnabotulinumtoxinA (BT-A) quarterly was the first treatment approved specifically for chronic migraine (CM). It is unclear whether three cycles are better than two to assess early BT-A response. We performed a retrospective analysis on real-life prospectively collected data in 16 European headache centers. All the centers provided data on patients treated with BT-A for CM over the first three cycles of treatment. For each treatment cycle we defined patients as "good responders" if reporting a ≥ 50% reduction in monthly headache days compared with the three months before starting BT-A, "partial responders" if reporting a 30-49% reduction in monthly headache days, and "non-responders" if reporting a < 30% reduction in monthly headache days or stopping the treatment before the third cycle. We included 2879 patients. Seven hundred and eighty-four (64.6%) of the 1213 patients reporting a good response during the first and/or the second cycle had a good response during the third cycle; 309 (49.3%) of the 627 patients reporting a partial response (but no good response) during the first and/or the second cycle had a good response during the third cycle; only 65 (6.3%) of the 1039 patients who did not respond during both the first two cycles achieved a good response during the third cycle. Multivariate analyses showed that partial or good response during the first or the second cycle were independently associated with good response during the third cycle. Our data suggest that patients with CM responding to BT-A during the first two cycles will likely benefit from the third cycle of treatment, while the probability that non-responders to the first two cycles start responding during the third cycle is low. These results can help guide the individual decision to stop or continue treatment after the second cycle in patients who have not responded to the first two cycles. The online version contains supplementary material available at 10.1007/s40122-021-00253-0.