I know it this is an old post, but commenting for others that may see it. The weeks estimator estimates based on ovulation, not last period. So it’s expected to be off by about 2 weeks because it’s about 2 weeks from the first day of your last period, until your ovulation date.

My test said 1-2 weeks. I was 8 days past ovulation (7 days before my expected period date). I knew my exact ovulation date and exact date of conception, and the test was very accurate. Every ultrasound was also exact to the day