It is difficult to determine exactly how long it will take to lose butt fat as it depends on a variety of factors such as diet, exercise routine, metabolism, and overall health. However, a safe and realistic rate of weight loss is typically 1-2 pounds per week. Therefore, if someone who weighs 150 pounds aims to lose butt fat specifically, it may take several weeks to a few months to see noticeable results. Consistency with a balanced diet and regular exercise targeting the glutes and lower body will be key in achieving the desired results.