Due Date Calculator – Estimate Your Baby's Due Date
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What Is a Due Date Calculator?
A due date calculator estimates when your baby is likely to be born, based on either the first day of your last menstrual period (LMP) or your conception date. It's the same method doctors use at your first prenatal visit to set an initial timeline.
Formula Used (Naegele's Rule)
From Last Period: Due Date = LMP + 280 days (40 weeks)
From Conception Date: Due Date = Conception Date + 266 days (38 weeks)
Naegele's rule assumes a regular 28-day cycle with ovulation around day 14. If your cycle is longer or shorter, your actual due date may shift by a few days — an ultrasound dating scan is the most accurate method your doctor will use to confirm it.
How to Use This Calculator
Choose whether you know your last period date or your conception date, select it from the calendar, then click "Calculate Due Date." You'll instantly see your estimated due date along with trimester milestones and your current week of pregnancy.
Only about 5% of babies are born exactly on their due date
Most babies arrive anywhere between 37 and 42 weeks. Think of your due date as the midpoint of a normal delivery window, not a fixed deadline.
Frequently Asked Questions
How accurate is a due date calculator?
It gives a reliable estimate based on average cycle length, but an early ultrasound is generally considered more accurate for confirming gestational age.
What if I don't know my last period date?
If you know your conception date instead (for example, from ovulation tracking or IVF), switch to the "Conception Date" option for a more direct estimate.
Can my due date change later in pregnancy?
Yes, your doctor may adjust it slightly after an early ultrasound, which measures the fetus directly rather than relying on cycle assumptions.
How is pregnancy week count related to my due date?
Pregnancy is typically counted from the first day of your last period, not the conception date, which is why it's counted as 40 weeks even though conception happens about 2 weeks later.