Pregnancy Due Date Calculator 🔒 Runs locally in your browser — nothing is uploaded.

Naegele's rule due date estimator

⚠ Please note

For informational purposes only — not medical advice. This is a statistical estimate; only about 5% of babies are born exactly on their due date. Always follow your healthcare provider's guidance for prenatal care and due-date estimates, which may use ultrasound dating that differs from this calculation.

The day your last period started — not when you think you conceived.

Defaults to today. Change it to see the gestational age on any other date.

Your estimate

Estimated due date
Estimated LMP
Gestational age
Trimester
Days until due date

Pregnancy progress

1st trimester2nd trimester3rd trimester

About this tool

Naegele's rule is the standard, decades-old method obstetric providers use for a first-pass due-date estimate: take the first day of your last menstrual period, add 280 days (40 weeks), and that is your estimated due date. It's a quick, consistent starting point — not a prediction of the exact day your baby will arrive. If you already know your due date or conception date, this calculator can work backward to estimate everything else, including how far along you are right now.

Pregnancy is typically divided into three trimesters: the first (weeks 1–13) covers early development and the initial wave of symptoms; the second (weeks 14–27) is often the most comfortable stretch; the third (week 28 onward) is the home stretch toward full term, generally considered 37 to 42 weeks. Every pregnancy is unique, and this estimate assumes a textbook 28-day cycle — your own care provider's ultrasound-based dating, and any adjustments they make along the way, should always take priority over this calculator.

Frequently asked questions

How accurate is a due date calculated this way?

It's a widely-used starting estimate, but statistically only about 5% of babies are actually born exactly on their calculated due date — most births happen within a window of roughly a week or two before or after it. Naegele's rule also assumes a "standard" 28-day cycle with ovulation on day 14, which doesn't match everyone's actual cycle — this is exactly why healthcare providers often refine the estimate using an early ultrasound measurement, which can be more precise for an individual pregnancy than calendar math alone.

What if I don't remember the exact first day of my last period?

This is common and completely understandable — try to recall your best estimate (even approximate is more useful than nothing), or if you know your due date or conception date from another source (like a prior doctor's estimate or fertility tracking), use the other two calculation modes this tool offers instead, which work from those dates directly. For anything beyond a rough personal estimate, an early-pregnancy ultrasound at a doctor's visit is the most reliable way to date a pregnancy regardless of LMP memory.