Pregnancy Weeks to Days Calculator | OhMyUnit

Type your gestational age in weeks + days. The tool tells you the total days, the current trimester, and how many weeks and days are left until 40 weeks.

Trimester	Weeks	Days
First	0 to 13 + 6	0–97
Second	14 + 0 to 27 + 6	98–195
Third	28 + 0 to 40 + 0	196–280

How obstetric weeks work

Pregnancy is dated from the first day of your last menstrual period (LMP), so at the time of conception you are already 2 weeks pregnant by convention. A full-term pregnancy is 40 weeks (280 days) from LMP, with 39–41 weeks considered "term".

Trimester boundaries (ACOG)

First trimester: 0 weeks 0 days through 13 weeks 6 days.
Second trimester: 14 weeks 0 days through 27 weeks 6 days.
Third trimester: 28 weeks 0 days through 40 weeks (or birth).

Reading "20 + 4"

Healthcare providers write gestational age as weeks + days. "20 + 4" means 20 weeks and 4 days, which is exactly 144 days from LMP.

This is informational only. Clinical dating uses an early ultrasound, which is more accurate than LMP-based estimates if your cycles are irregular.