BBT or Ovulation

Elizabeth

Hi I’m trying to understand. I plug my info into Premom because it seemed more accurate. But when I did my BBT this morning I noticed it jumped me to 4dpo and yesterday it was saying today is ovulation. Anyone have this happened? Yesterday I got my positive opk. Below is a pic of my charts. I know it’s just an estimate but seems weird. What day would be the 1st dpo?