Pregnancy Calculator

How the Pregnancy Calculator Works

The Pregnancy Calculator estimates your due date, gestational age, trimester, and pregnancy timeline using one of three starting points: your expected due date, the first day of your last menstrual period (LMP), or your estimated conception date. Internally, it converts whichever option you choose into a consistent reference LMP, then uses standard clinical rules to calculate your key dates and week-by-week progress.

Step 1: Establishing a Reference LMP

Everything begins with a normalized LMP (last menstrual period) date:

• If you start from LMP, that date is used directly.
• If you start from a known due date, the calculator counts back 280 days (40 weeks) to estimate the corresponding LMP.
• If you start from an estimated conception date, it counts back roughly 14 days (for a 28-day cycle) or adjusts using your provided cycle length to estimate LMP.

A configurable cycle length (typically 20–45 days) allows a simple adjustment for users who don't have a 28-day cycle, shifting the estimated conception and due date accordingly.

Step 2: Due Date, Gestational Age & Progress

Once the reference LMP is set, the calculator:

• Computes your estimated due date (EDD) as LMP + 280 days, adjusted for cycle length if applicable.
• Calculates gestational age today as full weeks and days between LMP and today's date.
• Determines your trimester based on current week: approximately weeks 1–13 (first), 14–27 (second), 28–40 (third).
• Shows pregnancy progress %, capped between 0% and 100% across the standard 40-week model.

This gives you an at-a-glance summary card with your key dates, current week, and how far along you are in the pregnancy timeline.

Step 3: Week-by-Week Timeline up to Week 42

To make the results easier to understand, the calculator builds a structured schedule:

• For each week (1–42), it shows the exact date range.
• Labels the trimester for that week.
• Includes high-level milestones such as early positive test window, common ultrasound windows, anatomy scan range, and term windows (early term, full term, late term).
• Highlights your current week so you can instantly see where today fits in the overall pregnancy.

This week-by-week output is designed for education and orientation—not to predict exact fetal development for every individual pregnancy.

What This Pregnancy Calculator Doesn't Do

To stay safe, transparent, and user-friendly, the tool intentionally doesnot:

• Replace ultrasound-based dating, clinical assessments, or any medical judgment.
• Fully adjust for IVF transfer protocols, multiples (twins, triplets), irregular or very long/short cycles, or high-risk pregnancies.
• Predict labor onset, fetal size, or health outcomes.

It provides general estimates based on average 40-week pregnancies and common clinical conventions. Always confirm due dates and concerns with your midwife, OB-GYN, or healthcare provider.

Educational Insight

Most people hear different dates—from apps, ultrasounds, and providers—and it can be confusing. By normalizing everything back to LMP and transparently showing how due dates, gestational age, and trimesters are calculated, this Pregnancy Calculator turns those moving pieces into a clear, consistent timeline you can understand and discuss confidently with your care team.