Eh, soalan ni memang common! Doctors biasanya hitung dari hari pertama last menstrual period (LMP) mu, bukan dari hari conception sebenarnya, so kalau LMP mu 20 Januari, that counts as week 1 pregnancy, even though baby baru conceive a few weeks later. A few of us mums were confused jugak at first, tapi doctor explain that's the standard way they calculate because kita tak selalu sure exactly when we ovulated kan. So basically, add 40 weeks from your LMP date dan tu lah your estimated due date!