Use our Pregnancy Due Date Calculator to estimate your baby’s arrival based on the first day of your last menstrual period (LMP) and your average cycle length. Get a quick Estimated Due Date (EDD), current gestational age, and a rough window for conception and trimester milestones.
How the Pregnancy Due Date Calculator works
The Pregnancy Due Date Calculator primarily uses Naegele’s rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). Because not everyone has a 28-day cycle, the tool also adjusts the calculation by adding or subtracting the difference between your average cycle length and 28 days. For example, if your cycles average 30 days, two extra days are added to your EDD; if they average 26 days, two days are subtracted.
What you’ll need
- The date your last period started (LMP)
- Your typical cycle length (most people are between 24 and 35 days; 28 is the standard)
What the calculator tells you
After you enter your information, the Pregnancy Due Date Calculator provides:
- Estimated Due Date (EDD): The most likely 40-week mark of pregnancy.
- Gestational age today: How far along you are in weeks and days, based on LMP and cycle-length adjustment.
- Estimated conception/ovulation date: A rough estimate based on your cycle; actual conception can vary.
- Trimester milestones: Approximate start of the second and third trimesters.
Why cycle length matters
Standard EDD calculations assume a 28-day cycle with ovulation around day 14. If your cycles are longer, you likely ovulate later; if shorter, you may ovulate earlier. Adjusting the due date by the difference from 28 days helps personalize the estimate. Still, every pregnancy is unique, and ultrasound dating in the first trimester can refine your EDD.
Irregular cycles
If your cycles vary a lot month to month, consider leaving the default 28 days or using an early ultrasound date from your healthcare provider for a more precise estimate. Tracking ovulation with tests or basal temperature can also improve accuracy for future calculations.
Understanding trimesters and key milestones
Pregnancy is often grouped into three trimesters:
- First trimester: Conception to 13 weeks + 6 days.
- Second trimester: 14 weeks to 27 weeks + 6 days.
- Third trimester: 28 weeks to birth.
Common milestones include the dating/viability scan in early weeks, the nuchal translucency window around 11–13 weeks, and the anatomy scan around 18–22 weeks. Your care team will tailor visit schedules and tests to your needs.
Limitations of due date estimates
Only about 5% of babies arrive on their exact due date. The EDD is best viewed as the center of a normal range. Most healthy births occur between 37 and 42 weeks. Factors such as irregular cycles, late ovulation, IVF timing, and ultrasound measurements can each shift the most accurate estimate. Always discuss your EDD with your clinician, especially if your ultrasound measurement differs from your LMP-based date.
How to get the most accurate EDD
- Use a reliable LMP date.
- Enter your typical cycle length if it differs from 28 days.
- Confirm with a first-trimester ultrasound when available.
- Share any tracking data (ovulation tests, temping) with your provider.
What to do next
Once you have your estimated due date, you can plan prenatal visits, nutrition, and maternity leave timelines. Keep in mind that your provider may update your EDD after reviewing ultrasound findings. Use this calculator as a helpful starting point, not a medical diagnosis.