Pregnancy Weeks Estimator

How accurate are the Clear Blue weeks estimator- in terms of actually predicting the weeks? According to my last period I should be 5 weeks today, however my clear blue predictor test said 1-2 weeks which would put me more at 3-4 weeks pregnant. This was the first month my husband and I tried to get pregnant after coming off birth control pills so to be honest, I am not sure how long my cycle would have been? Anyone else in this situation?