Pregnancy Due Date Calculator
A due date calculator estimates the expected delivery date using Naegele’s rule: 280 days (40 weeks) after the first day of the last menstrual period (LMP), the same estimate most clinicians start with. Naegele’s rule assumes a textbook 28-day cycle with ovulation on day 14, so the estimate shifts for people with longer or shorter cycles. An ultrasound-based estimate later in pregnancy is generally more precise than an LMP-only calculation, which this tool makes clear is a starting estimate, not a diagnosis.
Educational estimate only. Results are not medical, legal, or financial advice. Confirm important decisions with a qualified professional.
How it works
- Enter the first day of your last menstrual period.
- Read the estimated due date.
- See when the second and third trimesters are estimated to begin.
Formula Due date = LMP + 280 days
Frequently asked questions
How accurate is a due date from LMP?
It is a standard estimate; only about 5% of babies arrive exactly on the calculated date. An early ultrasound can refine it, especially for irregular cycles.
What if my cycle is not 28 days?
Naegele’s rule assumes a 28-day cycle with ovulation on day 14. If yours differs significantly, a clinician-adjusted or ultrasound-based estimate will be more accurate.
Is this the same as counting from conception?
No — this counts from LMP, which is about 2 weeks before typical conception, matching how due dates are conventionally quoted.
When do trimesters start?
This tool marks the second trimester at 13 weeks and the third at 27 weeks from LMP, common rounded conventions.
Is this medical advice?
No. It is an educational estimate — confirm dates and monitor the pregnancy with a qualified healthcare provider.