Due Date Calculator
Enter the first day of your last menstrual period to estimate your due date, current gestational age and trimester.
This estimate uses Naegele's rule (LMP + 280 days) and is not medical advice. Actual due dates vary — always confirm timing and gestational age with your doctor or midwife.
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How to use
- Enter the first day of your last menstrual period (LMP).
- View your estimated due date, calculated using Naegele's rule.
- If the date is in the past, see your current gestational age in weeks and days, and which trimester you're in.
What is this tool?
Due Date Calculator uses Naegele's rule — adding 280 days (40 weeks) to the first day of the last menstrual period — to estimate a pregnancy due date, the standard method used by most healthcare providers as a starting estimate. It also calculates gestational age and trimester based on today's date.
Common uses
- Getting a quick estimate of a pregnancy due date
- Tracking current gestational age in weeks and days
- Figuring out which trimester a pregnancy is currently in
- Preparing questions ahead of a prenatal appointment
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FAQ
How accurate is Naegele's rule?
It assumes a regular 28-day cycle and ovulation on day 14, so actual due dates commonly vary by a week or more. An ultrasound dating scan is generally more accurate, especially for irregular cycles.
Is this medical advice?
No. This is a simple estimate for general reference only. Always confirm your due date and gestational age with a doctor or midwife, who can use ultrasound measurements for a more precise estimate.
How are trimesters divided?
This calculator uses the common convention of weeks 1-13 for the first trimester, 14-27 for the second, and 28 onward for the third — though exact cutoffs vary slightly between sources.