Due Date Calculator — Free Pregnancy Due Date Estimator
A free due date calculator that estimates your baby's due date, current pregnancy week, and trimester in seconds — private, accurate, no sign-up needed.
Based on ACOG & Mayo Clinic guidelines · Last updated October 2026 · Read our medical disclaimer
How Does a Due Date Calculator Work?
This due date calculator estimates your baby's due date (EDD) using Naegele's Rule — the standard method recommended by the American College of Obstetricians and Gynecologists (ACOG) and used by doctors and midwives worldwide. The calculation adds 280 days (40 weeks) to the first day of your last menstrual period (LMP).
This method assumes a 28-day cycle and ovulation on day 14. If your cycle is longer or shorter, this pregnancy due date calculator automatically adjusts the estimate. According to Mayo Clinic, an early ultrasound (8–12 weeks) generally gives the most accurate dating if you're unsure of your LMP.
If you know your conception or ovulation date instead, the calculator adds 266 days — the average length of pregnancy measured from conception rather than LMP, since ovulation typically happens around day 14 of a cycle. If you have a recent ultrasound, the tool works backward from the scan's estimated gestational age to infer an implied LMP, then applies the same 280-day rule. Per ACOG, a first-trimester ultrasound is generally considered the most reliable dating method, especially if your cycles are irregular or you're unsure of your LMP.
The 3 Trimesters Explained
Frequently Asked Questions
How accurate is a due date calculator?
Only about 5% of babies are born exactly on their due date. Most babies arrive within 2 weeks before or after the EDD. A due date calculator gives a reliable estimate — your healthcare provider may adjust it based on your 12-week ultrasound scan.
What if I don't remember my last period date?
Use the "By Conception Date" or "By Ultrasound Date" method instead. Your dating scan (usually at 8–12 weeks) gives the most accurate due date.
When is a baby considered full term?
Per ACOG: early term is 37w0d–38w6d, full term is 39w0d–40w6d, late term is 41w0d–41w6d, and postterm is 42w0d or beyond. Babies born before 37 weeks are considered premature (preterm).
Can I use this pregnancy due date calculator for twins?
Yes, the LMP calculation works the same for twins. However, twin pregnancies are typically delivered earlier — around 36–38 weeks — so your actual delivery may be before the calculated date.
What method does this due date calculator use?
By default it uses Naegele's Rule (LMP + 280 days), the method recommended by ACOG (American College of Obstetricians and Gynecologists) and used by doctors and midwives worldwide. You can also calculate by conception date or ultrasound date for a potentially more precise estimate.
Once baby arrives, try our bedtime calculator or weight percentile tracker — free, just like this one.
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Current Progress
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Estimated Conception
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| 🌱 End of 1st Trimester (Week 12) | |
| ✨ End of 2nd Trimester (Week 27) | |
| 🌟 Full Term (Week 39) | |
| 🍼 Estimated Due Date (Week 40) |