Pregnancy Calculator
Calculate your due date and pregnancy milestones, or find your fertile window and ovulation day.
Pregnancy Due Date
Enter the first day of your last menstrual period (LMP) to calculate your due date and milestones.
How to Use the Pregnancy Calculator
- Enter the first day of your last menstrual period (LMP) — this is the standard starting point used by healthcare providers.
- Your estimated due date, current week of pregnancy, and trimester are calculated immediately.
- Scroll down to see key milestone dates for each trimester and important prenatal appointment windows.
- Use the Ovulation tab to calculate your estimated fertile window based on your average cycle length.
Pregnancy Week by Week: Key Milestones
First Trimester (Weeks 1–12)
The embryo implants and major organ systems begin forming. The heartbeat is detectable by ultrasound around week 6. Morning sickness is common. Your first prenatal appointment is typically scheduled between weeks 8–10.
Second Trimester (Weeks 13–26)
Often called the "golden trimester" — nausea typically eases and energy returns. The anatomy ultrasound (usually around week 20) checks for structural development. Fetal movement (quickening) is first felt between weeks 16–22.
Third Trimester (Weeks 27–40)
Rapid growth and final organ maturation. The baby's lungs mature and they gain most of their birth weight. Weekly appointments typically begin around week 36. Full term is considered 39–40 weeks.
Frequently Asked Questions
How is a due date calculated?
The standard method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. This method assumes a 28-day cycle and ovulation on day 14. Your healthcare provider may adjust the due date based on ultrasound measurements, which are typically more accurate in the first trimester.
How accurate is an estimated due date?
Only about 4–5% of babies are born on their exact due date. Most births occur within two weeks before or after the EDD. A due date is best thought of as the center of a birth window rather than a fixed deadline.
What if my cycle is longer or shorter than 28 days?
Naegele's Rule is calibrated for a 28-day cycle. If your cycle is consistently longer (e.g., 35 days), ovulation likely occurs later and your due date may be a week or so later than the standard calculation. The ovulation calculator on this tool adjusts for custom cycle lengths.
When should I confirm my due date with a doctor?
Always confirm your due date with your healthcare provider at your first prenatal visit. A first-trimester ultrasound (before 13 weeks 6 days) is the most accurate way to date a pregnancy and will be used to confirm or adjust the estimated due date.
Disclaimer: This calculator is for informational purposes only and does not constitute medical advice. Always consult your OB-GYN or midwife for personalized pregnancy care and an accurate due date.