Pregnancy Due Date Calculator

To calculate due date from LMP, use Naegele's Rule: Add 7 days to the first day of your last menstrual period (LMP), then subtract 3 months, and add 1 year. For example, if LMP was January 15, 2024: Add 7 days = January 22, 2024; Subtract 3 months = October 22, 2023; Add 1 year = October 22, 2024 (due date). Alternatively, simply add 280 days (40 weeks) to your LMP first day. Our free pregnancy calculator does this instantly - just enter your LMP date and average cycle length. The calculator assumes conception occurs about 14 days after LMP (for 28-day cycle) and pregnancy lasts 280 days from LMP. For irregular cycles, adjust cycle length in calculator for more accurate estimation. First trimester ultrasound (6-12 weeks) provides most accurate dating.

Pregnancy due date calculators provide estimates, not guarantees. Accuracy facts: (1) Only 4-5% of babies are born on exact due date, (2) About 70% are born within 10 days (before or after) of due date, (3) 90% are born within 2 weeks of due date, (4) First-time mothers often deliver 1-3 days late on average. Factors affecting accuracy: (1) Irregular menstrual cycles - makes LMP-based dating less reliable, (2) Uncertain LMP date - reduces calculation accuracy, (3) First trimester ultrasound (6-13 weeks) is most accurate method, accurate within 5-7 days, (4) Genetics - some families tend toward shorter/longer pregnancies. Full-term pregnancy is 37-42 weeks; delivery anywhere in this range is normal. Healthcare providers may induce labor if you reach 41-42 weeks to reduce risks.

Pregnancy divides into three trimesters, each about 13-14 weeks: FIRST TRIMESTER (Weeks 1-12): Baby development - All major organs form, heart begins beating week 5-6, baby grows to 2-3 inches. Mother experiences - Morning sickness, fatigue, breast tenderness, frequent urination. Key milestones - First prenatal visit, possible first ultrasound (8-12 weeks), genetic screening options. SECOND TRIMESTER (Weeks 13-26): Baby development - Rapid growth, gender visible on ultrasound (18-20 weeks), baby begins moving (felt 16-25 weeks), hearing develops. Mother experiences - Energy returns, "pregnancy glow," baby bump shows, feeling baby move (quickening). Key milestones - Anatomy scan ultrasound (18-22 weeks), glucose screening (24-28 weeks). THIRD TRIMESTER (Weeks 27-40): Baby development - Weight gain, lung maturity, baby positions for birth (head down), fat accumulation. Mother experiences - Increased fatigue, Braxton Hicks contractions, back pain, frequent urination returns. Key milestones - Weekly checkups (36+ weeks), Group B strep test (35-37 weeks), preparation for delivery.

If you can't remember your last menstrual period (LMP) date, several alternatives exist for determining due date: (1) EARLY ULTRASOUND - Most accurate method: Dating ultrasound (6-13 weeks) measures crown-rump length to estimate gestational age within 5-7 days; Later ultrasounds less accurate for dating. (2) CONCEPTION DATE - If you know conception date (from fertility tracking, IVF, or single intercourse): Add 266 days (38 weeks) to conception date for due date. (3) PREGNANCY SYMPTOMS - Less accurate but provides estimate: Count back from when pregnancy test turned positive; Symptoms typically appear 4-6 weeks after LMP. (4) hCG BLOOD LEVELS - Doctor can estimate weeks pregnant by hCG hormone levels, though ranges vary widely. (5) PHYSICAL EXAM - Healthcare provider may estimate based on uterus size, though less precise. Most reliable approach: Schedule early prenatal visit for dating ultrasound if LMP unknown. Accurate dating is important for proper prenatal care timing and delivery planning.

Pregnancy duration counting can be confusing because it's measured from your last menstrual period (LMP), not conception. Here's how it works: COUNTING METHOD: Pregnancy is 40 weeks or 280 days from first day of LMP; You're actually pregnant from conception, which occurs about 2 weeks after LMP; So when you're "4 weeks pregnant," baby is actually 2 weeks old since conception. CALCULATING YOUR WEEKS: Count days from first day of last period to today; Divide by 7 for weeks pregnant; Example: LMP was 63 days ago = 9 weeks pregnant. PREGNANCY PHASES BY WEEKS: Weeks 1-4: Often unaware, positive test around week 4-5; Weeks 5-12: First trimester, morning sickness common, major development; Weeks 13-26: Second trimester, energy returns, baby movements felt; Weeks 27-40: Third trimester, preparing for birth; Week 37-42: Full term, delivery likely. DUE DATE: Set at 40 weeks from LMP; Normal range is 37-42 weeks (full term). Our calculator instantly shows your current week, trimester, days pregnant, and due date - just enter your LMP date.