Calculate your due date and pregnancy week
👶 Your Pregnancy Journey Pregnancy lasts about 40 weeks (280 days) from your last menstrual period. Most babies arrive between 37-42 weeks. This calculator uses the standard Naegele's rule: add 1 year to your LMP, subtract 3 months, add 7 days.
Naegele's rule, the formula behind most due-date estimates, was named after a German obstetrician in the 1800s — and it's still the standard starting point doctors use today, over 200 years later.
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This calculator uses Naegele's rule, the standard method for estimating due dates. For natural conception, add 1 year to your last menstrual period (LMP), subtract 3 months, then add 7 days. Pregnancy is considered full-term at 39-40 weeks. For IVF pregnancies, the calculation starts from the embryo transfer date instead, since conception timing is already precisely known.
First Trimester (Weeks 1-12): Critical development period, morning sickness common. Second Trimester (Weeks 13-26): Often called the "golden trimester" — more energy, baby movements felt. Third Trimester (Weeks 27-40): Final growth spurt, preparing for birth.
Only about 5% of babies arrive on their exact due date. First babies often arrive later. Cycle length affects accuracy — longer cycles mean later ovulation, which is why this calculator lets you adjust for it. This tool provides an estimate, not a guarantee; your healthcare provider will confirm timing with ultrasound measurements.
Use this as a planning tool, not a diagnosis. Schedule your first prenatal visit around weeks 8-12. Remember that a "due month" is more realistic than a "due day" — most healthy pregnancies last 37-42 weeks. Always follow your healthcare provider's guidance for prenatal care.
Example: Say your last menstrual period started on January 1, 2026, with a typical 28-day cycle and natural conception. Applying Naegele's rule: add 1 year → January 1, 2027, subtract 3 months → October 1, 2026, add 7 days → October 8, 2026 is your estimated due date.
It's an estimate based on Naegele's rule, not a guarantee. Only about 5% of babies are born on their exact due date, so treat this as a due month, not a due day.
Yes, for natural conception. A longer cycle usually means ovulation happened later, which shifts the estimated due date later too. That's why this calculator lets you enter your typical cycle length.
Yes. IVF due dates are calculated from the embryo transfer date instead of the last menstrual period, since the exact conception timing is already known.