Pregnancy Calculator
Track due date and trimesters based on last menstrual period.
How does the pregnancy calculator work?
The pregnancy calculator uses Naegele's rule — the standard method used by obstetricians. It adds 280 days (40 weeks) to the first day of your last menstrual period (LMP) to estimate the due date. It also determines how many weeks pregnant you are today, and which trimester you're in: 1st trimester (weeks 1–13), 2nd trimester (weeks 14–26), or 3rd trimester (week 27 until delivery). This gives you a clear timeline of your pregnancy journey.
How to use the Pregnancy Calculator
Select the first day of your last menstrual period using the date picker. Click "Calculate" to instantly see your estimated due date, how many weeks pregnant you are, and your current trimester. The calculation assumes a regular 28‑day cycle — for irregular cycles, consult your doctor for a personalized due date.
Example calculation
If your last period started on January 1, 2025, your estimated due date is October 8, 2025 (280 days later). On June 1, 2025, you would be about 21 weeks pregnant and in your 2nd trimester. The calculator updates all these numbers automatically based on today's date.
Frequently Asked Questions
Is the due date from this calculator accurate?
Naegele's rule is the standard estimation method, but only about 5% of babies arrive on their exact due date. Most are born within two weeks before or after. Use this date as a helpful guideline and discuss your personalized timeline with your healthcare provider.
What if I don't know my last period date?
If you're unsure of your LMP, an early ultrasound is the most reliable way to determine gestational age and estimate your due date. Many health authorities also offer pregnancy tracking apps that can help you log your cycle for future reference.