Due Date Calculator
Estimate your due date, trimester timeline, and conception window from your last menstrual period.
Trimester Dates
| Trimester | Start Date | End Date |
|---|---|---|
| First Trimester | -- | -- |
| Second Trimester | -- | -- |
| Third Trimester | -- | -- |
What is Due Date Calculator?
A Due Date Calculator estimates the expected delivery date of a baby based on the first day of the mother's last menstrual period (LMP) and her average cycle length. The standard method, known as Naegele's rule, assumes a 28-day cycle and adds 280 days to the LMP. This calculator adjusts for cycles that are longer or shorter than 28 days for a more personalized estimate.
In addition to the due date, the calculator provides a conception window, fetal age, and the date ranges for each trimester. These insights help expectant parents prepare for prenatal care, schedule important screenings, and understand the stages of pregnancy.
How to Use
- Enter the first day of your last menstrual period.
- Enter your average cycle length in days (default is 28).
- Click Calculate Due Date to see your estimated due date and conception window.
- Review the trimester dates table to understand the timeline of your pregnancy.
Frequently Asked Questions
What is Naegele's rule?
Naegele's rule estimates the due date by adding one year, subtracting three months, and adding seven days to the first day of the last menstrual period, assuming a 28-day cycle.
How does cycle length affect the due date?
Longer cycles usually mean ovulation occurs later, so the due date is pushed back. Shorter cycles move the due date earlier. This calculator adds or subtracts days based on the difference from 28 days.
When is the conception window?
Conception typically occurs within a few days around ovulation, which is roughly 14 days before the next expected period. The calculator shows an estimated 5-day fertile window.
How accurate is a due date calculator?
Due date estimates are approximate. Only about 4% of babies are born on their exact due date. Early ultrasound measurements provide the most accurate dating.