When does initial fat re-absorption occur after BBL? When does fat "take" on average?

The results immediately following surgery will be the largest due to swelling and lack of fat resorption.  The buttocks will continue to decrease in size for the first few weeks.   I have observed that between 4 and 6 weeks the buttocks tend to stabilize in volume.  Usually by 3 months, the swelling is minimal and totally resolved by 6 months.  
Kenneth Hughes, MD, Board Certified Plastic Surgeon
Los Angeles, CA

Hello thank you for your excellent question. Typically, due to swelling and lack of reabsorption early in your recovery, you will see the biggest changes in your buttocks in the days/week right after your surgery. As a general rule of reabsorption/graft survival (and results are variable depending on techniques, surgeons and patients) following a Brazilian butt lift, about 50% of the fat and cellular population transferred and grafted will be lost over the next few weeks to month after your surgery. At around the 4-6 month mark is where what is left is generally there surviving and carrying on. This is where post-op pictures should be taken and assessed. Also keep in mind the results will remain best if your weight is stable as the fat cells grafted to your buttocks can still swell and shrink depending on your weight. Best of results!

While fat takes within the first several days after transfer, swelling will mask the exact volume for several weeks.