If I have lipo for a BBL, how badly will the skin sag? Will I need a tummy tuck? (Photos)

Even with the stretch marks, you have age on your side. Your skin will contract. The stretch marks won’t go away but the goal is a flatter more sculpted version of you. The lipo approach to the front of your abdomen should be a bit conservative to respect the tissue. A more aggressive approach can be taken to the sides aka silhouette. Consult with experienced lipo plastic surgeons. Discuss you goals and concerns.

It would not be accurate to make a definite judgment without an in-person examination, but based on your description and photo, there appears to be some skin laxity and stretch marks on the abdomen. These usually indicate that the skin’s elasticity is partially reduced after pregnancy.
In such cases, liposuction can sometimes make looseness more visible because removing fat decreases the support underneath the skin. However, since you are young, your skin still has some capacity to retract, so the degree of sagging may remain moderate.
A tummy tuck would provide the most comprehensive correction for stretched skin, but if you are planning to have more children, postponing that procedure makes sense. For now, a conservative liposuction combined with BBL can be done safely if your expectations are realistic and the surgeon applies a gentle, controlled technique to protect the skin’s quality.
It is best to be examined in person so your surgeon can assess skin tone, tissue thickness, and elasticity before deciding on the right approach.
— Güray Yesiladali, MD

Based on the photos you've shared, I can see the stretch marks which can indicate some loose skin. However, like you said you are 20 and looking to have more children in the future. There is another option for you which can yield good results which include liposuction with skin tightening. At my office, we have the latest skin tightening technology called Quantum which we can use to help contour your abdomen as well. This procedure can be combined with a BBL as well. Don't hesitate to schedule a consult with us!

The photos show that you already have stretch marks and some skin laxity. You also likely have some abdominal wall laxity from pregnancy which is not affected by liposuction. If you are intending to have more children it's recommended to wait until you've completed your family before having a tummy tuck. Once you are ready a tummy tuck will get you the most optimal results. It will address excess skin, subcutaneous fat as well as correct the abdominal muscle.

Based on only two post photos, I recommend a virtual consultation for better understanding your body type hard to predict if you will have irregular, wrinkle, dented skin following liposuction I might recommend combination of a Lipo 360 with abdominal J plasma or Endo laser in addition to the BBL. Again, best of virtual concert with expect fees to range from $6000-$10,000.