conception and due date calculator

What this calculator does

This conception and due date calculator gives you an estimated due date, likely conception date, and a simple pregnancy timeline. It is designed to be practical: you can calculate from your last menstrual period, a known conception date, or IVF transfer date.

Most pregnancies are dated from the last menstrual period (LMP), not the exact conception day. That means gestational age typically starts about two weeks before conception in a 28-day cycle.

How due date estimation works

1) From LMP (most common)

This method uses Naegele's rule: add 280 days (40 weeks) to the first day of your LMP. If you enter your average cycle length, the calculator also estimates conception by assuming ovulation occurs about 14 days before your next period.

• Due date estimate: LMP + 280 days
• Conception estimate: LMP + (cycle length - 14)

2) From known conception date

If you know when conception likely happened, this method adds 266 days (38 weeks). This aligns with the average interval from conception to birth.

• Due date estimate: Conception + 266 days

3) From IVF transfer date

IVF dating can be more precise because transfer timing is known. The calculator estimates conception based on embryo age and then projects the due date.

• Estimated conception: Transfer date - embryo age (3 or 5 days)
• Due date estimate: Estimated conception + 266 days

How accurate is a due date?

An estimated due date is a target, not an exact prediction. Many healthy pregnancies deliver between 37 and 42 weeks. Cycle variability, implantation timing, and individual differences can shift the timeline.

Ultrasound measurements in early pregnancy are often used to confirm or adjust dates. If your provider gives a different estimated due date than a calculator, follow your provider's guidance.

Pregnancy timeline highlights

• ~12 weeks: End of first trimester approaching
• ~20 weeks: Mid-pregnancy anatomy scan window
• ~24 weeks: Viability milestone often discussed clinically
• ~39 weeks: Full-term range commonly referenced
• 40 weeks: Estimated due date

Tips for better estimates

• Use the earliest reliable date you have (LMP, confirmed conception, or IVF transfer).
• Enter your true average cycle length instead of defaulting to 28 days if your cycles are regular and different.
• Recheck your dates after your first prenatal visit and ultrasound.
• Track symptoms and milestones, but rely on your care team for diagnosis and decisions.

Important medical note

This tool is educational and informational. It cannot diagnose pregnancy viability, labor onset, or complications. If you have bleeding, severe pain, reduced fetal movement, contractions, or any urgent concern, contact your healthcare provider immediately.