Pregnancy Calculator

Expecting? This pregnancy calculator estimates your due date, tells you how many weeks pregnant you are, and gives you a timeline of key milestones — from first heartbeat to full term.

How to Use This Calculator

1. Select your calculation method: Last Menstrual Period (LMP), conception date, IVF transfer date, or ultrasound date.
2. Enter the relevant date.
3. Enter your average cycle length (default 28 days) if using LMP method.
4. Click Calculate to see due date, current gestational age, and trimester milestones.

How Due Date Is Calculated

The standard method uses Naegele's rule:

Due Date = LMP + 280 days (40 weeks)

Pregnancy is counted from the first day of the last menstrual period, not from conception (which typically occurs about 2 weeks after LMP).

For cycles other than 28 days: Due Date = LMP + 280 days ± (cycle length − 28 days)

Pregnancy Timeline

• Week 6: Heartbeat detectable by ultrasound
• Week 10: End of embryonic period; fetal period begins
• Week 12: End of first trimester; risk of miscarriage decreases significantly
• Week 20: Anatomy ultrasound; gender often detectable
• Week 24: Viability threshold (survival possible with intensive care)
• Week 28: End of second trimester / start of third
• Week 37: Early term
• Week 39–40: Full term
• Week 40+: Post-term (induction often considered at 41–42 weeks)

Common Mistakes to Avoid

• Treating the due date as exact — Only ~5% of babies arrive on their exact due date. Full-term pregnancy spans weeks 39–41. The due date is an estimate, not a deadline.
• Counting weeks differently than OBs do — Medical professionals count from LMP (gestational age). If your provider says "8 weeks pregnant," that's 8 weeks from LMP — about 6 weeks from conception.

Frequently Asked Questions

How accurate is a due date calculated from LMP?

LMP-based due dates have ±2 week accuracy. Early ultrasound (6–10 weeks) is more accurate — within a few days. Later ultrasounds are less reliable for dating.

What is gestational age vs. fetal age?

Gestational age counts from LMP (standard medical dating). Fetal age (embryonic age) counts from conception — usually about 2 weeks less. Medical providers always use gestational age.

What if my cycle isn't 28 days?

Longer cycles delay ovulation, pushing the due date later. Shorter cycles advance ovulation, making the due date earlier. This calculator adjusts for your actual cycle length.

Conclusion

Knowing your due date helps you plan prenatal care, prepare your home, and track your pregnancy week by week. Use this calculator for an evidence-based estimate — and confirm with your OB or midwife at your first appointment.

Related: Due Date Calculator | Pregnancy Weight Gain Calculator | Ovulation Calculator | Conception Calculator