How to Use the Pregnancy Calculator
Enter your last menstrual period (LMP) to instantly see your current gestational age in weeks and days, your trimester, estimated due date, and countdown to delivery. This tool uses Naegele's rule β the standard medical formula for estimating due dates.
Trimester Guide
- 1st Trimester β Weeks 1β12 (organ formation, morning sickness)
- 2nd Trimester β Weeks 13β27 (feel fetal movement, stable period)
- 3rd Trimester β Weeks 28β40 (rapid growth, birth prep)
How Due Date Is Calculated
Naegele's rule: due date = LMP + 280 days (40 weeks). This assumes a regular 28-day cycle with ovulation on day 14. If your cycle length differs, your actual due date may vary. Your OB/GYN's ultrasound dating takes priority.
Frequently Asked Questions
Ultrasound dating measures fetal size directly and is considered more accurate, especially if your LMP is uncertain or your cycle is irregular. Always use the date confirmed by your doctor.
Naegele's rule assumes a 28-day cycle. If yours is longer (e.g., 35 days), ovulation occurs later and your due date may be shifted by the difference. Your provider can adjust using LMP and ultrasound data.
No. This calculator provides an estimate for informational purposes only. Always confirm with your healthcare provider for accurate dating and prenatal care.