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Due Date Calculator

Knowing your estimated due date helps you and your healthcare provider plan for prenatal care and delivery. This calculator supports three methods: last menstrual period (LMP), known conception date, and IVF transfer date. All methods provide an estimated due date along with your current week of pregnancy and trimester.

Quick Answer

Your estimated due date is 280 days (40 weeks) from the first day of your last menstrual period using Naegele's rule.

These results are estimates based on general formulas and are not a substitute for professional medical advice. Consult a healthcare provider before making health decisions.

Select a method and enter a date above to calculate your estimated due date.

How the Formula Works

  1. Choose your calculation method: LMP, Conception Date, or IVF Transfer Date.

    Method determines the starting point and offset

  2. LMP method: Add 280 days to your last menstrual period date. Adjust for cycle length if different from 28 days.

    EDD = LMP + 280 + (cycleLength - 28)

  3. Conception method: Add 266 days to the known conception date.

    EDD = conception date + 266 days

  4. IVF method: Add 261 days to the 5-day embryo transfer date.

    EDD = transfer date + 261 days (5-day embryo)

  5. Calculate current pregnancy progress by finding the number of days since the equivalent LMP date (EDD minus 280 days).

    Weeks pregnant = days since start / 7

Limitations

  • Due date calculations are estimates and only about 5% of babies are born on their exact due date. Most births occur within a two-week window around the estimated date.
  • The LMP method assumes ovulation on day 14 of a 28-day cycle. If your cycle length differs, the adjustment may not perfectly reflect your actual ovulation date.
  • The IVF calculation assumes a 5-day (blastocyst) embryo transfer. If you had a 3-day transfer, consult your fertility specialist for a more precise estimate.
  • Ultrasound dating, especially in the first trimester, is generally more accurate than LMP-based calculations and may result in a different due date.
  • This calculator is for informational purposes only and does not replace professional prenatal care or ultrasound-based dating.

Frequently Asked Questions

How is my due date calculated from my last period?
The LMP method adds 280 days (40 weeks) to the first day of your last menstrual period. If your cycle length is different from 28 days, the calculator adjusts by adding or subtracting the difference. For example, a 30-day cycle adds 2 extra days.
Which due date method is most accurate?
First-trimester ultrasound is generally the most accurate method. Among calculator methods, the conception date method can be very accurate if you know the exact date. The LMP method is most commonly used but depends on regular cycles. IVF dates are precise because the transfer date is known exactly.
What are the three trimesters of pregnancy?
The first trimester spans weeks 1-13, the second trimester covers weeks 14-27, and the third trimester begins at week 28 and continues until delivery. Each trimester involves different stages of fetal development and maternal changes.
Why does cycle length affect my due date?
The standard LMP calculation assumes a 28-day cycle with ovulation on day 14. If your cycle is longer, ovulation likely occurred later, pushing the due date further out. If shorter, ovulation occurred earlier, bringing the due date closer.
Can my due date change during pregnancy?
Yes. Your healthcare provider may adjust your due date based on ultrasound measurements, especially if there is a significant discrepancy between the ultrasound estimate and the LMP-based date. First-trimester ultrasounds are the most reliable for dating.

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