How long before seroma is considered healed? I'm 3 weeks post op mini tummy tuck.

It depends. A seroma is a fluid
collection that can occur after a tummy tuck.  If it is very small usually
it will go away on its own.  If the fluid collection is larger it can
become painful and can become infected and will need to be treated.  If it
is not infected then sometimes it can be drained with a needle.  Once it
is infected, usually this will require a more aggressive procedure that
requires a longer term drainage catheter to be placed. Once the fluid is
drained, depending on how long it was there, the body will heal typically in
4-6 weeks.  However, if the seroma was large and or present for a long
time and or there was an infection, the healing for this will be longer.  Additionally,
if the seroma continues to recur after drainage then sometimes another surgical
procedure is needed to remove the scar tissue from the seroma (called a seroma
capsule).
 

Generally, if you have gone a few days without seeing reaccumulation of fluid, you are unlikely to have another seroma.  If you do not have any fluid collecting, then you can assume the leaking lymphatic channels are healing and the skin and soft tissue are now becoming more adherent to the fascia overlying the muscles.  The healing between the skin flap and the abdominal wall, obliterating the space where a seroma would collect, is immature and may be tenuous, so I agree with my colleagues that it is still important to wear compression and avoid movements that would cause shearing between the soft tissue and the muscle.  Best wishes for an easy recovery!