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Pregnancy Calculator — Due Date, Weeks Pregnant & Trimester

Calculate your due date, current week of pregnancy, trimester, and key milestones. Based on last menstrual period or conception date. Free pregnancy tracker.

This calculator provides estimates based on Naegele's rule. Due dates are estimates — only 4% of babies are born on the calculated date. Always consult your healthcare provider for accurate pregnancy dating and prenatal care.
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What is the Pregnancy Calculator?

This pregnancy calculator estimates your due date, current week and trimester of pregnancy, and tracks key milestones from conception to birth. It supports three input methods: last menstrual period (LMP), conception date, or a known due date — and uses standard obstetric Naegele's rule for all calculations.

Pregnancy Calculator Formula

From LMP: Due Date = LMP + 280 days; Conception Date = LMP + 14 days From Conception: Due Date = Conception + 266 days; LMP = Conception − 14 days From Due Date: LMP = Due Date − 280 days; Conception = Due Date − 266 days Weeks Pregnant = days from LMP to today ÷ 7 (rounded down) Trimester: weeks 1–13 = First; weeks 14–27 = Second; weeks 28+ = Third

Pregnancy Calculator Example

LMP January 1, 2025: Conception Date = January 15, 2025. Due Date = October 8, 2025. At 20 weeks (around May 15): Second Trimester, anatomy scan due. At 28 weeks (around July 9): Third Trimester begins.

How to Use the Pregnancy Calculator

  1. 1Select your input method: Last Menstrual Period (most common), Conception Date (if known), or Known Due Date (from a previous scan or OB visit).
  2. 2Enter the date in YYYY-MM-DD format or use the date picker. All calculations are relative to today's date.
  3. 3Click Calculate to see your estimated due date, weeks pregnant, trimester, days remaining, and a full milestone timeline from your pregnancy start to birth.

Frequently Asked Questions

How is the due date calculated?
The due date is calculated using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This is equivalent to subtracting 3 months and adding 7 days to the LMP date. For example, an LMP of January 1 gives an estimated due date of October 8. This rule assumes a standard 28-day cycle with ovulation on day 14.
How accurate is the due date?
Only about 4% of babies are actually born on their calculated due date. A normal full-term pregnancy ranges from 37 to 42 weeks, so a window of roughly ±2 weeks around your due date is entirely normal. Early ultrasound (especially before 13 weeks) can provide more accurate dating than LMP alone, particularly if your cycles are irregular.
What are the three trimesters?
Pregnancy is divided into three trimesters: the First Trimester covers weeks 1–13 and includes the embryonic period, organ development, and the highest risk of miscarriage; the Second Trimester covers weeks 14–27 and is often the most comfortable phase, with the anatomy scan around week 20; the Third Trimester covers weeks 28–40+ and involves rapid growth, lung maturation, and preparation for birth.
What if I don't know my LMP?
If you don't know the date of your last menstrual period, you can use your estimated conception date if you know it. Otherwise, an early ultrasound (ideally in the first trimester) is the most accurate way for your healthcare provider to establish a gestational age and estimated due date. You can also use a known due date from a previous scan.
What does '40 weeks pregnant' mean?
Pregnancy duration is counted from the first day of your last menstrual period — not from conception. Since ovulation and conception typically occur around day 14 of the cycle, you are technically about 2 weeks pregnant before conception even happens. This means a 40-week pregnancy includes approximately 38 weeks of actual fetal development. 'Full term' is defined as 37–42 weeks; babies born before 37 weeks are considered preterm.

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Trusted Sources & Methodology

↗World Health Organization (WHO) — Global health standards and BMI classifications
↗Centers for Disease Control (CDC) — US health guidelines and population data
↗National Institutes of Health (NIH) — Medical research and clinical guidelines
↗Mayo Clinic — Trusted clinical information and health advice

API Access

Coming Soon
https://api.solviqlab.com/v1/pregnancy-calculator

REST API for developers. Integrate this tool into your app.

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