Calculate your estimated due date (EDD) from your last menstrual period or conception date.
This tool estimates your expected delivery date based on the first day of your last menstrual period (LMP) or the date of conception, using standard obstetric dating conventions. It's intended as a general estimate — actual delivery dates commonly vary by a couple of weeks in either direction.
This calculator commonly uses Naegele's Rule: Due Date = LMP + 280 days (40 weeks), assuming a standard 28-day cycle with ovulation around day 14. If conception date is known instead, 266 days is added directly.
Enter the first day of your last menstrual period (or your conception date if known), and the calculator estimates your expected due date.
Example: If your last period began on January 1, your estimated due date would be around October 8 of the same year (280 days later).
How accurate is this due date estimate? Only about 5% of babies are actually born on their exact calculated due date — most births occur within a two-week window before or after, so treat this as a general estimate rather than a precise prediction.
Why is 280 days used instead of the actual ~266-day gestation period? Because the exact ovulation and conception date is often unknown, due dates are conventionally calculated from the last menstrual period instead, which adds roughly two extra weeks compared to counting from conception directly.
Does an irregular cycle affect the accuracy of this calculation? Yes, this standard calculation assumes a 28-day cycle with ovulation on day 14; individuals with longer, shorter, or irregular cycles may have a less accurate estimate from this method alone.
Will my doctor use a different method to confirm my due date? Often yes — early pregnancy ultrasounds can provide a more precise dating estimate based on fetal measurements, which may adjust the initially calculated due date from LMP.
Should I make major plans based solely on this calculated date? It's best used as a general planning reference; since actual delivery timing varies naturally, flexibility around the estimated date is generally recommended for practical planning purposes.