Comprehensive Dating Tool

Pregnancy Calculator

Calculate your estimated due date, current pregnancy week, trimester, and milestones based on standard clinical obstetrical models.

Calculate Your Pregnancy

Enter the first day of your last menstrual period (LMP) to view your estimated due date, gestational age, and current trimester.

First day of last period (LMP)RequiredThe first day of bleeding during your last menstrual cycle.

Average cycle lengthOptionalStandard calculations assume a 28-day cycle with ovulation on day 14.

Estimated Due Date

May 12, 2027

224 days remaining until this estimated date

Gestational Age

8 weeks

In your 9th week

Trimester

Trimester 1

Weeks 1–13

Estimated Conception

August 19, 2026

Approx. ovulation window

Progress

20%

of 40 weeks completed

Journey: Week 1Week 8Week 40

Week 8 Baby Size Comparison: Raspberry

Webbed fingers and toes begin to separate into distinct digits. The eyelids and external ear folds form, and early involuntary movements begin.

* Note: Fruit & seed comparisons are playful visual metaphors, not clinical measurements.

Estimated Key Milestones

Conception WindowAugust 19, 2026

End of 1st Trimester (13w 6d)November 10, 2026

Halfway Mark (20w Anatomy Scan)December 23, 2026

End of 2nd Trimester (27w 6d)February 16, 2027

Full Term (37 Weeks)April 21, 2027

Estimated Due Date (40 Weeks)May 12, 2027

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A quick note on estimated dates: Due dates are guidelines. Only about 4% to 5% of babies arrive on their exact calculated due date, while about 80% arrive within two weeks before or after. Your midwife or doctor may refine your estimated due date following your early ultrasound dating scan.

The Science of Dating

How Pregnancy Weeks Are Calculated

Understanding the difference between gestational age and conception age brings clarity to your timeline.

Naegele's Rule (280 Days)

Clinically, pregnancy is measured from the first day of your last menstrual period (LMP), not the date of conception. A standard gestation spans 40 weeks, which equals 280 calendar days.

Gestational vs. Conception Age

Because ovulation typically happens about 14 days after your period starts, your baby is conceived about 2 weeks into your counted gestational age. When you are 4 weeks pregnant, your baby has been growing for approximately 2 weeks.

Trimester Boundaries

According to ACOG standards, Trimester 1 covers weeks 1–13. Trimester 2 covers weeks 14–27. Trimester 3 starts at week 28 and continues until delivery.

Common Questions

Pregnancy Calculation FAQ

Reliable, evidence-based answers to frequently asked questions about gestational dating and timelines.

How is a pregnancy due date calculated?

Medical providers calculate estimated due dates using Naegele's rule: by adding 280 days (40 weeks) to the first day of your last normal menstrual period (LMP). If your menstrual cycle is regularly longer or shorter than the standard 28-day model, the calculation can be adjusted accordingly.

How many weeks is a full-term pregnancy?

A full-term pregnancy is generally considered 40 weeks (280 days) from your LMP. Medical guidelines classify babies born between 37 weeks and 38 weeks and 6 days as 'early term', between 39 weeks and 40 weeks and 6 days as 'full term', and 41 weeks to 41 weeks and 6 days as 'late term'.

How are pregnancy weeks counted?

Pregnancy weeks describe completed weeks plus extra days. For example, if you are at '12 weeks, 3 days', you have completed 12 full weeks and are currently experiencing your 13th week of pregnancy.

What is the difference between gestational age and conception age?

Gestational age is measured from the first day of your last period, before ovulation and fertilization actually occur. Conception age (fetal age) begins at the moment the egg is fertilized, which typically takes place approximately 14 days after your period. Gestational age is standard in medical obstetrics.

Can my healthcare provider give me a different due date?

Yes, and this is completely normal. An early first-trimester ultrasound dating scan (crown-rump length measurement) provides the most precise estimate of fetal development. If there is a notable discrepancy between your LMP date and the ultrasound measurement, your clinician will update your official estimated due date.

How accurate is an estimated due date?

Only about 4% to 5% of babies arrive precisely on their estimated due date. It is best considered an estimated arrival window; roughly 80% of healthy infants are born within a two-week window before or after the estimated date.