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Due Date Calculator — Calculate Your Baby's Due Date by LMP or Conception

Calculate your pregnancy due date using last menstrual period, conception date, or IVF transfer date. Get trimester dates and key milestones. Free & accurate.

Due date calculations are estimates based on Naegele's rule. Actual birth may occur 2–3 weeks before or after the estimated date. Ultrasound measurements are more accurate for pregnancy dating. Always follow your healthcare provider's guidance.
Calculation Method

What is the Due Date Calculator?

This due date calculator estimates your baby's expected birth date using four methods: last menstrual period (LMP), conception date, IVF day-3 embryo transfer, or IVF day-5 blastocyst transfer. It also shows your current gestational age, trimester, trimester end dates, and a full timeline of key pregnancy milestones — all calculated using standard obstetric formulas.

Due Date 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 IVF Day-3 Transfer: Due Date = Transfer + 263 days; LMP = Transfer − 17 days From IVF Day-5 Transfer: Due Date = Transfer + 261 days; LMP = Transfer − 19 days Gestational Age = days from LMP to today ÷ 7 (weeks) + remainder (days) Trimester 1: weeks 1–13 | Trimester 2: weeks 14–27 | Trimester 3: weeks 28+

Due Date Calculator Example

LMP January 1, 2025: Due Date = October 8, 2025 (280 days later). Conception Date = January 15, 2025. At 20 weeks (around May 15): Second Trimester, anatomy scan due. IVF day-5 blastocyst transfer January 15, 2025: Due Date = October 3, 2025 (261 days later). The transfer date shifts the calculation because the embryo's exact age is known at the time of transfer.

How to Use the Due Date Calculator

  1. 1Select your calculation method: LMP (most common for natural pregnancies), Conception Date (if known), IVF Day-3, or IVF Day-5 blastocyst transfer.
  2. 2Enter the relevant date using the date picker. All results are calculated relative to today's date.
  3. 3Click Calculate to see your estimated due date, gestational age, trimester, trimester end dates, days remaining, and a complete milestone timeline from your pregnancy start to birth.

Frequently Asked Questions

How is the due date calculated from LMP?
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 standard method has been used in obstetrics since the 1850s and assumes a regular 28-day cycle with ovulation on day 14. For example, an LMP of January 1, 2025 gives an estimated due date of October 8, 2025.
How accurate is the due date?
Only about 4% of babies are born on their exact calculated due date. A normal full-term pregnancy ranges from 37 to 42 weeks, so a window of roughly ±2 weeks is entirely normal. Early ultrasound (especially before 13 weeks) is more accurate than LMP dating, particularly if your cycles are irregular. The due date is a clinical estimate, not a precise prediction.
How do IVF due dates differ from natural conception?
For IVF pregnancies, the embryo's age is already precisely known at the time of transfer. For a day-3 embryo transfer, the due date is calculated as transfer date + 263 days (because the embryo is already 3 days old). For a day-5 blastocyst transfer, it is transfer date + 261 days. This adjusted calculation is more accurate than LMP dating for IVF pregnancies.
What is gestational age vs fetal age?
Gestational age is counted from the first day of your last menstrual period (LMP), not from conception. Since ovulation typically occurs around day 14 of the cycle, the fetal age (time since conception) is approximately 2 weeks less than the gestational age. Doctors use gestational age as the standard — so at 12 weeks gestational age, the fetus is approximately 10 weeks old.
When does each trimester start and end?
The first trimester covers weeks 1–13 and includes the embryonic period and organ development. The second trimester covers weeks 14–27 and is often the most comfortable phase, with the anatomy scan typically at week 20. The third trimester covers weeks 28 through birth at week 40 (or beyond). Some sources define second trimester as starting at week 13+1; the boundaries used here follow the most common clinical convention.

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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

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https://api.solviqlab.com/v1/due-date-calculator

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

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