Pregnancy Calculator - Track Gestational Progress & Milestones

Pregnancy Calculator – Track Gestational Age & Milestones

Preparing for a new arrival is an extraordinary journey. From the moment of a positive test, tracking pregnancy week by week helps in understanding how the baby is developing and what changes to expect.

This calculator takes the first day of the last menstrual period (LMP) and generates a complete gestational timeline: gestational age in weeks and days, an estimated due date (EDD) at 40 weeks (280 days), an estimated conception date at LMP + 14 days, the current trimester, and a baby-size analogy comparing growth to familiar fruits and vegetables.

How Pregnancy Weeks Are Counted

In clinical obstetrics, pregnancy is dated from the first day of the last menstrual period (LMP) rather than the date of conception. During weeks 1 and 2, the body is preparing for ovulation — technically not pregnant yet, but these two weeks are still included in the standard 40-week count. Conception typically occurs around day 14 of a standard 28-day cycle, when a sperm fertilizes the released egg. Implantation in the uterine lining generally follows around weeks 3 to 4.

Calculation Formulas Used by the Code

Total Days = Current Date - LMP Date

Gestational Weeks = ≤ftlfloor (Total Days / 7) rfloor, quad Remaining Days = Total Days bmod 7

Estimated Due Date (EDD) = LMP Date + 280 days

Estimated Conception Date = LMP Date + 14 days

Trimester Progress Breakdown

First Trimester (weeks 1–12) covers implantation, rapid cell division, organ formation, and the first heartbeat. Second Trimester (weeks 13–26) covers fetal growth, early movements ("quickening"), and hearing development. Third Trimester (weeks 27–40) covers lung maturation, rapid weight gain, brain activity, and birth preparation.

Developmental Milestones and Baby Size Scale

Worked Examples

Example 1: LMP of January 1, 2026

EDD = Jan 1, 2026 + 280 days = Thu Oct 08 2026. Estimated Conception = Jan 1, 2026 + 14 days = Thu Jan 15 2026. The week 12 milestone (Lime) falls on Thu Mar 26 2026, and the week 20 milestone (Banana) falls on Thu May 21 2026.

Example 2: LMP of March 15, 2026

EDD = Mar 15, 2026 + 280 days = Sun Dec 20 2026. Estimated Conception = Mar 15, 2026 + 14 days = Sun Mar 29 2026. The week 12 milestone (Lime) falls on Sun Jun 07 2026, and the week 20 milestone (Banana) falls on Sun Aug 02 2026.

Why Ultrasound Dates May Differ

If a first-trimester dating ultrasound is performed, the scan date may differ slightly from the LMP-based calculation. LMP calculations assume a 28-day cycle with ovulation on day 14; if ovulation actually occurred earlier or later, an ultrasound measuring the baby's crown-rump length (CRL) provides a more precise clinical due date.

What This Calculator Does Not Include

Frequently Asked Questions

Why does pregnancy age start 2 weeks before conception occurs?

Because the exact day of ovulation and fertilization is difficult to pinpoint in natural conception, obstetricians worldwide use the first day of the Last Menstrual Period (LMP) as a reliable standardized starting marker instead.

What is the difference between an LMP due date and an ultrasound due date?

An LMP calculation assumes a standard 28-day cycle with ovulation on day 14. A first-trimester dating ultrasound measures the embryo's crown-rump length (CRL) directly, which can adjust the due date if the actual cycle was shorter or longer than average.

How are pregnancy trimesters divided?

First Trimester covers weeks 1 through 12, Second Trimester covers weeks 13 through 26, and Third Trimester covers weeks 27 through 40.

Does the due date ever change as the pregnancy progresses?

The LMP-based due date calculated here stays fixed once the LMP date is entered. In clinical practice, a due date can be adjusted after a dating ultrasound if it indicates the pregnancy is more or less advanced than the LMP alone suggests.