What is a Due Date Calculator?
A due date calculator estimates when your baby will be born based on when your pregnancy began. The most common method uses your last menstrual period (LMP) and adds 280 days (40 weeks) to estimate your due date—this is called Naegele's Rule.
Keep in mind: your due date is an estimate, not a guarantee. Only about 5% of babies arrive exactly on their due date. Most babies are born within two weeks before or after the estimated date. It's better to think of it as a "due window."
Multiple Calculation Methods
LMP, conception date, IVF transfer, or ultrasound measurements
Trimester Tracking
Know which trimester you're in and what to expect
Week-by-Week Progress
See exactly how far along you are in days and weeks
Important Milestones
Key dates for appointments and screenings
Key pregnancy terms to understand:
- Gestational age — Weeks pregnant, counted from first day of last period
- Fetal age — Actual age of embryo/fetus (about 2 weeks less than gestational)
- First trimester — Weeks 1-12 (highest risk period, major organ development)
- Second trimester — Weeks 13-26 (often called the "honeymoon period")
- Third trimester — Weeks 27-40 (final growth and preparation for birth)
Pregnancy Timeline & Milestones
Here's what happens during each phase of pregnancy and important dates to remember:
First Trimester (Weeks 1-12)
Weeks 1-4: Conception occurs, embryo implants in uterus. Most women don't know they're pregnant yet.
Weeks 5-8: Heart starts beating (week 6). Morning sickness often begins. First prenatal appointment.
Weeks 9-12: All major organs forming. First trimester screening (nuchal translucency). Risk of miscarriage drops significantly after week 12.
Second Trimester (Weeks 13-26)
Weeks 13-16: Energy often returns. Belly starts showing. Baby can hear sounds.
Weeks 17-20: Anatomy scan (usually week 18-22). May feel first movements (quickening). Can often find out baby's sex.
Weeks 21-26: Baby gains weight rapidly. Glucose screening test (week 24-28). Viability milestone around week 24.
Third Trimester (Weeks 27-40)
Weeks 27-32: Baby's lungs developing. More frequent checkups. May experience Braxton Hicks contractions.
Weeks 33-36: Baby moves into head-down position. Group B strep test (weeks 35-37). Nesting instinct kicks in.
Weeks 37-40: Considered "full term" at 39 weeks. Baby drops lower (lightening). Watch for signs of labor.
When to Call Your Doctor
Contact your healthcare provider if you experience: vaginal bleeding, severe abdominal pain, severe headaches with vision changes, signs of preterm labor (regular contractions before 37 weeks), decreased fetal movement, or any symptoms that worry you. Trust your instincts.