Congrats on starting your new credit journey !!! Remember, it's an endurance race, not a sprint. I think you'll be able to get over 600 easily, and 620 should not be too difficult. It really depends on how old your derogs are, who their with, and what kind they are (CC, medical, student loans, etc...). I'm going to bet you'll be surprised how quickly you can meet your initial goals. Just don't get down if you reach a wall at some point in the future. Everyone does. It usually starts out quickly, getting some derogs removed, scores jumping up, and than you get to the 2nd stage where things slow down, as you have some derogs that your having issues with. It happens. Just stay in the game. In a few short year's, everything will be positive, and you'll be looking at 750+ goals. Best of luck. Keep us updated.
