I weigh 150 lbs. my goal is to lose 20 lbs which would be 22.5% of my body weight. how much could this lower my bp?? i walk too.

Estimate: Various studies have documented various degrees of improvement. A drop by 12 points in the systolic and up to 8 points in the diastolic were noted in the following study with the loss of 8kg (about 18 lb.) http://www.ncbi.nlm.nih.gov/pubmed/15107009# Keep in mind other factors such as sodium restriction and effects of other conditions and meds are a factor too.