Due Date Calculator
Estimate your pregnancy due date, track trimester timelines, calculate gestational age, and map out milestones using LMP, conception, IVF, or ultrasound metrics.
1. Estimation Method
Current Progress
Fetal Timeline Milestones
🤰 Understanding Due Dates, Conception, and Milestones
In modern obstetrics, establishing a baseline pregnancy timeline is critical to monitoring fetal growth, scheduling screenings, and managing labor delivery dates. Because fertilization dates are rarely known precisely in natural conception, clinicians historically relied on the **First Day of the Last Menstrual Period (LMP)** combined with standard mathematical rules to schedule dates.
How standard pregnancy calculations work
A full-term human pregnancy is clinically assumed to last approximately **280 days** (40 weeks) from the first day of the last menstrual period, or **266 days** (38 weeks) from the date of conception. These time windows are calculated using three standard models:
- Naegele's Rule: The historic standard calculation method. It estimates the due date by adding 1 year, subtracting 3 calendar months, and adding 7 days to the first day of the last menstrual period.
- Cycle Length Adjustments: Since Naegele's rule assumes a standard 28-day cycle with ovulation on day 14, women with shorter or longer menstrual cycles require corrections. For example, a 32-day cycle pushes the estimated due date out by an additional 4 days.
- Assisted Reproductive Technology (IVF): IVF transfers provide an exact physiological date. Gestation is calculated as 266 days from conception, meaning we subtract the specific embryo culture phase (3 days or 5 days) from the transfer day to calculate due date.
Trimesters & Milestone Markers
Once your estimated due date is set, the developmental timeline is broken down into three trimesters:
• **First Trimester (Weeks 1 to 12):** A period of rapid cellular division and major organ formation.
• **Second Trimester (Weeks 13 to 26):** Fetal skeleton development and movement. Fetal viability (the statistical threshold where a baby could survive outside the womb with intensive care) is generally reached around **24 weeks**.
• **Third Trimester (Weeks 27 to 40):** Final weight gain, lung maturation, and preparation for birth. Full term is achieved at **37 weeks**, meaning the baby is fully formed and ready for a safe delivery.