Your Estimated Due Date
December 25, 2026
Friday
This estimate is informational only and not medical advice. Confirm your care plan with a qualified prenatal professional. Read our disclaimer.
How Your Due Date is Estimated
The due date calculation is an estimation based on standard pregnancy lengths. The method varies depending on the input you provide.
- Last Menstrual Period (LMP) Method: This is the most common method. It assumes a standard 28-day menstrual cycle and ovulation on day 14. The estimated due date is calculated by adding 280 days (40 weeks) to the first day of your LMP.
- Conception Date Method: If you know the exact date of conception, the calculator adds 266 days (38 weeks) to this date. This is the average length of a pregnancy from the moment of conception.
Current progress (gestational age) is calculated from the start of the LMP (either the actual date or an approximation if using conception date) to today. Trimesters are divided as follows: 1st (0-13 weeks), 2nd (14-27 weeks), and 3rd (28+ weeks).
Example Calculation
Based on your inputs, here's how the estimation was made:
- Calculation Method: Last Menstrual Period
- Date Provided: March 20, 2026
We added 280 days (40 weeks) to your LMP date, March 20, 2026, to estimate your due date as December 25, 2026.
Counting from March 20, 2026 to today gives 0 days, which is 0 full weeks and 0 extra days. That places the pregnancy in trimester 1.
How it works
This tool applies Naegele-style date arithmetic: EDD = LMP + 280 days (40 weeks) or, when conception is known, EDD = conception + 266 days (38 weeks). Gestational age is counted from the pregnancy start date to today, then split into weeks and days.
Worked real-world examples
- Regular 28-day cycle: LMP on Jan 10, 2026 leads to an estimated due date of Oct 17, 2026 (280 days later).
- IVF transfer with known conception timing: conception on Mar 2, 2026 leads to an estimated due date of Nov 23, 2026 (266 days later).
- Early prenatal intake: if LMP was 9 weeks and 3 days ago, the tool reports 9w3d and places the pregnancy in trimester 1.
Common mistakes
- Using the last day of bleeding instead of the first day of LMP.
- Entering implantation date, positive test date, or intercourse date as conception date.
- Assuming this estimate replaces dating ultrasound when cycles are irregular.
When not to use this tool
- When bleeding dates are uncertain or cycles are highly irregular.
- For pregnancies with provider-adjusted dating (for example, IVF protocols or corrected ultrasound dating).
- For medical decision-making without clinician review.
Sources and standards
- Naegele's rule conventions for LMP-based due date estimation.
- ACOG guidance on estimating due date and first-trimester ultrasound-based refinement.
Frequently Asked Questions
Find answers to common questions about this calculator below.
Other Date & Lifecycle Calculators
LMP Twelve Weeks Ago
Someone attending their first trimester appointment using the first day of their last period.
LMP Date: December 26, 2025
Today: March 20, 2026
12w 0d
Gestational Age
Oct 2, 2026
Estimated Due Date
How the calculation is done
- Start with the first day of the last menstrual period on December 26, 2025.
- Add 280 days (40 weeks) to reach the estimated due date of October 2, 2026.
- Count 84 days from December 26, 2025 to today. That equals 12 full weeks and 0 extra days, placing the pregnancy in trimester 1.
Known Conception Date
A pregnancy with a documented conception date from fertility tracking or IVF treatment.
Conception Date: January 9, 2026
Approximate LMP: December 26, 2025 (14 days earlier)
Today: March 20, 2026
12w 0d
Gestational Age
Oct 2, 2026
Estimated Due Date
How the calculation is done
- Start with the conception date on January 9, 2026. We approximate the LMP as December 26, 2025.
- Add 266 days (38 weeks) to reach the estimated due date of October 2, 2026.
- Count 84 days from December 26, 2025 to today. That equals 12 full weeks and 0 extra days, placing the pregnancy in trimester 1.