Finding out your estimated due date is one of the most exciting moments of pregnancy. Our free due date calculator uses Naegele's rule — the same method your doctor uses — to estimate when your baby will arrive based on your last menstrual period or conception date. Get your trimester timeline, gestational age, and key milestones instantly.
A pregnancy due date calculator estimates the expected date of delivery (EDD) based on the start of your last menstrual period (LMP) or a known conception date. The standard method, Naegele's rule, assumes a 280-day (40-week) pregnancy from the first day of the LMP. This includes approximately 2 weeks before conception (since ovulation typically occurs around day 14 of a 28-day cycle). While only 5% of babies arrive on their exact due date, the EDD provides a critical reference point for prenatal care scheduling, milestone tracking, and delivery planning.
Due date calculation from LMP or conception date. Cycle length adjustment for non-standard cycles. Current gestational age in weeks and days. Trimester identification and timeline. Key milestone dates throughout pregnancy. Countdown to due date. Conception date estimation from LMP. Support for multiple date formats. Mobile-friendly for appointment reference. Complete privacy — no data stored. No registration required.
Using the LMP method: the calculator adds 280 days (40 weeks) to the first day of your last menstrual period. If your cycle length differs from 28 days, it adjusts by the difference (e.g., a 32-day cycle adds 4 extra days to the due date). Using the conception date method: it adds 266 days (38 weeks) from the known date of conception. The calculator then determines your current gestational age, identifies your trimester, and generates a timeline of important dates including viability milestones, anatomy scan window, and term boundaries.
Personal Planning — Knowing your due date for maternity leave, nursery preparation, and family announcements. Prenatal Care — Scheduling appointments, tests, and screenings at appropriate gestational ages. Work Planning — Arranging maternity or paternity leave dates. Travel Planning — Knowing when to avoid flying (most airlines restrict after 36 weeks). Birth Plan Preparation — Timing childbirth classes and hospital tours. Family Coordination — Helping relatives plan visits around the expected arrival. IVF Dating — Calculating due dates from known embryo transfer dates.
Our calculator provides the same Naegele's rule calculation your healthcare provider uses, with the added benefit of cycle length adjustment and milestone tracking. It is completely free, requires no sign-up, and processes everything locally — your pregnancy information is never stored or shared. While this tool provides an excellent estimate, always confirm your due date with your healthcare provider, who can use ultrasound measurements for the most accurate dating.
Newly pregnant individuals wanting to estimate their due date. Couples planning for the arrival of their baby. Anyone who wants to understand pregnancy milestones and timing. People undergoing IVF who want to calculate from transfer date. Healthcare students learning about pregnancy dating. Anyone curious about gestational age and trimester boundaries.
Recall the first day of your last menstrual period — this is the most commonly used date for calculation. Enter it into the calculator. If your cycle is not 28 days, enter your average cycle length for a more accurate estimate. Review your estimated due date, current gestational week, and trimester. Note the milestone dates for your prenatal care timeline. Schedule your first prenatal appointment (typically 8–10 weeks). Remember: confirm your EDD with your doctor at your first ultrasound.
Use LMP Date Accurately — The first day of bleeding, not spotting. Adjust for Cycle Length — Irregular or long cycles shift the due date. Confirm With Ultrasound — An 8–12 week ultrasound is the most accurate dating method. Track by Gestational Age — Medical professionals count from LMP, not conception. Plan Within a Window — Expect delivery 38–42 weeks, not on the exact date. Keep Your Provider Informed — Share this estimate but follow their official dating. Do Not Change Due Date Late — Early dating is most accurate; later ultrasounds are less reliable.
The LMP method assumes regular cycles and ovulation on day 14 — accuracy decreases for irregular cycles. Only 5% of babies arrive on the exact due date; 80% arrive within 2 weeks. The calculator cannot account for individual variations in implantation timing or fetal development. Early ultrasound measurements (8–12 weeks) are more accurate than LMP-based calculation. This tool provides estimates only — always consult your healthcare provider for medical decisions. Not intended as a substitute for professional prenatal care.
The standard method uses Naegele's rule: take the first day of your last menstrual period (LMP), add 1 year, subtract 3 months, and add 7 days. This assumes a 28-day cycle with ovulation on day 14, giving a 280-day (40-week) pregnancy. For example, if your LMP was January 1, your due date would be October 8. If your cycle is longer or shorter than 28 days, the calculator adjusts by adding or subtracting the difference. Conception-based calculation adds 266 days (38 weeks) from the date of conception.
LMP-based calculations are accurate within ±2 weeks for women with regular 28-day cycles. Only about 5% of babies arrive on their exact due date. About 80% are born within 2 weeks of the estimated date (38–42 weeks). Early ultrasound dating (8–12 weeks) is more accurate, with a margin of ±5 days. Later ultrasounds become less accurate for dating. If ultrasound and LMP dates differ by more than 7 days, most providers will adjust the due date to match the ultrasound.
First Trimester (Weeks 1–12): Embryo development, organ formation, morning sickness common, highest miscarriage risk. Second Trimester (Weeks 13–27): Often called the 'golden period,' baby movements felt (quickening), anatomy scan at 18–22 weeks, energy returns. Third Trimester (Weeks 28–40): Rapid fetal growth, Braxton Hicks contractions, nesting instinct, prenatal visits increase to weekly. Full term is 39–40 weeks; early term is 37–38 weeks; babies born before 37 weeks are premature.
If your cycle is longer than 28 days, ovulation likely occurs later, and your due date shifts forward accordingly. For a 35-day cycle, ovulation is approximately day 21 (not day 14), so the due date moves 7 days later. For shorter cycles (e.g., 24 days), ovulation occurs earlier and the due date moves forward. Our calculator lets you input your actual cycle length to adjust the calculation. Very irregular cycles make LMP dating less reliable — early ultrasound dating is recommended in those cases.
Gestational age counts from the first day of the last menstrual period (LMP) — this is what your doctor uses and what pregnancy apps track. It includes about 2 weeks before conception actually occurred. Fetal age (conceptional age) counts from the actual date of fertilization, so it is about 2 weeks less than gestational age. A baby at '12 weeks pregnant' (gestational age) has actually been developing for about 10 weeks (fetal age). Medical records and milestones always use gestational age.
Most healthcare providers schedule the first prenatal visit between 8–10 weeks gestational age. Call your provider immediately if you experience: severe abdominal pain, heavy bleeding, severe dizziness, or fever above 100.4°F. At the first visit, expect confirmation of pregnancy, dating ultrasound, blood work, medical history review, and discussion of prenatal vitamins. If you have a history of complications, ectopic pregnancy, or certain medical conditions, earlier evaluation may be recommended.
Week 6: Heartbeat detectable on ultrasound. Week 8: All major organs forming. Week 12: Risk of miscarriage drops significantly; end of first trimester. Week 16: Baby's sex may be visible on ultrasound. Week 20: Anatomy scan; halfway point; mother feels movement. Week 24: Viability milestone — baby has survival chance outside womb. Week 28: Third trimester begins; eyes open. Week 37: Early term — lungs mature. Week 39: Full term — optimal delivery window. Week 40: Due date. Week 41+: Post-term; induction usually discussed.
Yes, due dates can be revised. The most common reason is discrepancy between LMP dating and early ultrasound measurements. If the ultrasound at 8–12 weeks shows a due date more than 7 days different from LMP calculation, most providers adopt the ultrasound date. Due dates are NOT changed based on later ultrasounds (after 20 weeks) because fetal size variation increases as pregnancy progresses. Once established, your official due date typically stays fixed even if subsequent measurements suggest slight differences.