How far along?

Hi!! I recently found out that I’m pregnant but my doctor isn’t having me come in until the end of January. I’m a little confused about how far along I am. My last period started November 30th, so going by that date I’m only 3 weeks, 1 day. But I know I conceived December 7th (short cycle) so going by this date, it says I’m 4 weeks 1 day. Different apps are saying different things so im a little confused!