Accurately calculate your estimated due date (EDD) and follow fetal milestones using standard menstrual history, conception timing, IVF details, or ultrasound CRL.
Menstrual Cycle Length28 days
20 days28 days (Default)45 days
Estimated Due Date
Thursday, January 28, 2027
Current Gestational Age
12 Weeks, 0 Days
1st Trimester (Weeks 1 - 12)
Days Left
196
until Delivery
Fetal Milestones Timeline
Hover over any timeline marker to view calculated milestone dates and descriptions.
Medical Disclaimer:This calculator is for educational and informational purposes only. It is not intended to substitute for professional medical advice, diagnosis, or clinical evaluation. Due dates are estimates only; only 4-5% of births occur on the exact date. Always consult your obstetrician or healthcare professional to verify dating and track your baby's development.
Clinical Standards & Sources:
American College of Obstetricians and Gynecologists (ACOG) — Dating guidelines (280 days from LMP baseline).
Determine your estimated date of delivery (EDD) and follow your pregnancy progress. Compare dates using standard clinical methods like Naegele's rule, Parikh's cycle adjustment, IVF details, or first-trimester ultrasound.
Mathematical Formula & Logic
The due date is standardly calculated as 280 days from the last menstrual period (LMP) or 266 days from conception.
When cycles differ from 28 days, Parikh's formula adjusts the due date: Due Date = LMP + 280 days + (CycleLength - 28 days).
For IVF, due dates are established from embryo transfer dates:
- Day 3 Transfer: Due Date = Transfer Date + 263 days
- Day 5 Transfer: Due Date = Transfer Date + 261 days
First-trimester ultrasound scans calculate gestational age from crown-rump length (CRL) in millimeters using the Robinson & Fleming formula:
Gestational Age (days) = 8.052 × √CRL + 23.73 days.
Step-by-Step Example
Worked Examples:
1. LMP Method: For an LMP of January 1, 2026 and a cycle length of 30 days:
Effective LMP = Jan 1 + (30 - 28) = Jan 3, 2026
Due Date = Jan 3 + 280 days = October 10, 2026
2. Ultrasound Method: An ultrasound scan on March 1, 2026 showing a CRL of 16 mm:
Gestational Age = 8.052 × √16 + 23.73 = 8.052 × 4 + 23.73 = 32.208 + 23.73 = 55.938 days (~8 weeks 0 days)
Estimated Due Date = March 1, 2026 - 56 days + 280 days = October 23, 2026
Reference Data & Values
method
baseline gestation
cycle adjustment
Last Menstrual Period (LMP)
280 days (40 weeks)
Cycle Length - 28 days
Conception Date
266 days (38 weeks)
None (ovulation assumed Day 14)
IVF Day 3 Transfer
263 days from transfer
None (Day 3 in vitro adjustment)
IVF Day 5 Transfer
261 days from transfer
None (Day 5 in vitro adjustment)
First-Trimester Ultrasound (CRL)
Based on Robinson & Fleming formula
Formula: 8.052 * sqrt(CRL) + 23.73 days
Frequently Asked Questions
Due dates are standardly calculated by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP), assuming a regular 28-day menstrual cycle.
Parikh's formula adjusts Naegele's rule for cycle lengths other than 28 days by adding or subtracting the variance: Due Date = LMP + 280 days + (Cycle Length - 28 days).
IVF due dates are calculated based on the embryo transfer date: add 263 days for a day 3 transfer, and 261 days for a day 5 transfer.
In the first trimester, ultrasound measurements of crown-rump length (CRL) in millimeters are converted to gestational days using the Robinson & Fleming equation: Gestational Age = 8.052 * sqrt(CRL) + 23.73.
Ovulation times can vary, meaning conception may happen earlier or later than day 14. First-trimester ultrasound measurements are considered the clinical standard for establishing the due date when they differ from LMP calculations.
A standard human pregnancy is calculated as 280 days (40 weeks) from the LMP, or 266 days (38 weeks) from conception.
A pregnancy is considered early term at 37 weeks, full term starting at 39 weeks, and late term at 41 weeks. Deliveries before 37 weeks are considered preterm.
Due dates are rarely changed after the first trimester unless a significant growth discrepancy is detected, because early ultrasound measurements are the most accurate.