What does your BMI need to be prior to a tummy tuck? That is a very good question. Generally, the rule is a BMI of 30. However, everyone is different and everyone carries their weight differently. You will have to undergo a personal examination by a board certified plastic surgeon to have your question answered definitively.
If a patient has excess loose skin to the point of having an apron of skin hanging down (called a panniculus), a simple excision of this panniculus could be done with a BMI of 40 or less. The patient would then have to lose weight down to a BMI of 30 to have their full tummy tuck, with muscle plication, etc.. A panniculectomy, in my experience, in this situation has given patients an incentive to lose more weight, and this plan has been successful in my practice.
I greatly prefer, however, for a patient to have a BMI of 30 or less because the entire tummy tuck procedure, with liposuction and muscle repair can be performed, and their recovery is easier and complication rate is lower.
I hope this has helped you with your question. Best of luck to you, and stick to lean meat and healthy vegetables, and you should have no problems losing weight. Stay away from simple carbohydrates, such as bread, potatoes, rice, pasta, and certainly desserts.