How accurate is the pregnancy due date?

Only about 5% of babies are born exactly on their due date. Most are born within 2 weeks before or after—anywhere from 38-42 weeks is considered full term. Due date calculations assume a 28-day cycle with ovulation on day 14, but cycles vary. First-trimester ultrasounds (especially before 13 weeks) provide more accurate dating than last menstrual period (LMP), with accuracy within 5-7 days. Due dates are estimates for planning purposes. First-time mothers often deliver slightly later than second+ pregnancies.

How do you calculate pregnancy weeks and trimesters?

Pregnancy is calculated from the first day of your last menstrual period (LMP), even though conception occurs about 2 weeks later. This makes pregnancy approximately 40 weeks or 280 days. First trimester is weeks 1-12, second trimester is weeks 13-26, third trimester is weeks 27-40. Weeks are grouped into months differently than calendar months—pregnancy months are about 4.3 weeks each. Healthcare providers track by weeks for more precision. You're considered full term at 39-40 weeks, early term at 37-38 weeks.

What are important pregnancy milestones?

Key milestones include: Week 4-5: positive pregnancy test; Week 6-8: first ultrasound sees heartbeat; Week 10-13: end of first trimester, reduced miscarriage risk; Week 12-13: nuchal translucency screening; Week 16-22: anatomy scan ultrasound; Week 18-25: feel baby movement (earlier in second+ pregnancies); Week 24: viability milestone; Week 28: third trimester begins; Week 36: weekly checkups begin; Week 37: early term; Week 39-40: full term; Week 41-42: possible induction discussion. Each milestone provides important development and health information.

Should I use LMP or conception date for calculation?

Medical professionals use LMP (last menstrual period) as the standard because it's a concrete date most women remember, while exact conception date is usually unknown (sperm can survive up to 5 days). If you know your exact conception date (from fertility treatment or certain ovulation date), you can calculate from that by adding 266 days (38 weeks) instead of 280 days (40 weeks) from LMP. However, early ultrasound measurements supersede both LMP and conception-based calculations for dating accuracy. Always confirm due date with your healthcare provider.

Date & Time

Pregnancy Calculator

Calculate your due date and see your pregnancy timeline.

How to Use This Calculator

Enter Last Menstrual Period Date

Input the first day of your last menstrual period (LMP). This is the standard starting point for pregnancy dating, even though conception typically occurs about 2 weeks later.

Or Enter Conception Date

If you know your exact conception date (from fertility treatment or confirmed ovulation), you can use this instead of LMP for a more accurate calculation. The calculator will adjust the timeline accordingly.

Or Enter Due Date

If your healthcare provider has given you a due date (often based on early ultrasound), you can work backward to see current week and upcoming milestones.

View Pregnancy Timeline

Review your estimated due date, current week of pregnancy, current trimester, and important upcoming milestones like screening dates, when you might feel movement, and when you reach full term. Use this to plan appointments and track development.