Track your pregnancy week by week. Get your due date, current trimester, and key milestones from your last period.
Pregnancy due dates are typically calculated using Naegele's Rule, which estimates the expected date of delivery (EDD) based on the first day of your last menstrual period (LMP). The standard formula adds 280 days (40 weeks) to the LMP, which accounts for approximately 2 weeks before conception actually occurs.
The formula: EDD = LMP + 280 days. If your menstrual cycle is longer or shorter than the average 28 days, the calculator adjusts accordingly. For each day your cycle differs from 28, the due date shifts by one day. This adjustment accounts for the fact that ovulation typically occurs 14 days before the next period begins.
Three trimesters: The first trimester (weeks 1-12) is when the baby's major organs begin forming and morning sickness is common. The second trimester (weeks 13-26) is often called the "honeymoon phase" as energy returns and the baby's movements become noticeable. The third trimester (weeks 27-40) involves rapid growth and preparation for delivery.
Important milestones: Viability (around 24 weeks) is when the baby has a chance of survival outside the womb with medical support. At 28 weeks, the baby can typically breathe with assistance. Full term is considered 39-40 weeks. Only about 5% of babies are born on their exact due date — most arrive within two weeks before or after.
Medical disclaimer: This calculator provides estimates only. Your healthcare provider may adjust your due date based on ultrasound measurements, especially in the first trimester. Always follow your doctor's guidance for prenatal care and important medical decisions.
Type the first day of your last period. This is the standard reference date used by obstetricians to track pregnancy progress.
The calculator shows your current week (1-40), which trimester youre in, and your estimated due date. It also lists key milestones like the first heartbeat and viability.
See important dates: first prenatal visit, anatomy scan window, viability (24 weeks), full term (37 weeks), and due date (40 weeks).
For related calculations, try our pregnancy due date calculator.
Cross-checked against authoritative formulas (IRS, NIST, ACM) and updated for 2025/2026 tax years and rates.
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Estimates only. Calculator results are for educational and planning purposes — not professional advice. For binding decisions on taxes, investments, health, or legal matters, consult a qualified professional.
FAQ
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The first trimester ends at week 13, the second at week 27, and the third at week 40 (or whenever you deliver). Our pregnancy calculator shows your current week and trimester. The first trimester has the highest miscarriage risk; the second is usually the easiest; the third is when the baby gains the most weight. Our pregnancy calculator tracks milestones like the first heartbeat (week 6), viability (week 24), and full term (week 37).
How it works
Our pregnancy calculator lets you find out how many weeks pregnant you are and what to expect at each stage, in three steps.
Type the first day of your last menstrual period (LMP). This is the standard reference date used by clinicians.
Type the typical length of your cycle in days. Use 28 if you are not sure.
The calculator shows your current week and day of pregnancy, the trimester you are in, the estimated due date, and key milestones coming up.