Pregnancy Due Date Calculator
Estimate your pregnancy due date based on your last period and cycle length.
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Enter your values and click Calculate
How It Works
The calculator determines your ovulation date by subtracting the luteal phase length from the total cycle length to find the follicular phase duration, then adding those days to your LMP date. Since human gestation from ovulation is approximately 266 days (38 weeks), that number is added to the estimated ovulation date to produce the EDD. For gestational age, today's date is compared against an adjusted LMP — anchored 14 days before the calculated ovulation — which is how medical convention counts gestational weeks. This approach gives a more accurate estimate than the fixed 280-day rule for people with non-standard cycles.
Examples
Standard 28-Day Cycle
A woman with a textbook 28-day cycle and 14-day luteal phase.
Result: Calculates an estimated due date exactly 280 days from the LMP (October 8, 2026).
Longer 35-Day Cycle
A woman with a longer 35-day cycle where ovulation happens later.
Result: Adjusts the due date forward to account for the later ovulation (October 15, 2026).
Short Luteal Phase
A 28-day cycle but with a shorter 10-day luteal phase.
Result: Adjusts the ovulation date later into the cycle, moving the due date to October 12, 2026.
Frequently Asked Questions
How accurate is a due date calculator?
Calculators provide an excellent baseline, but only about 4-5% of babies are born exactly on their estimated due date. Most babies arrive anywhere between 37 and 41 weeks of pregnancy.
What is LMP?
LMP stands for Last Menstrual Period. When calculating pregnancy, doctors ask for the FIRST day of your most recent period to use as a baseline starting point.
What if I have irregular cycles?
If your cycles fluctuate wildly, an LMP-based calculation might not be highly accurate. In cases of irregular periods, a first-trimester ultrasound is considered the most accurate way to date a pregnancy.
Why does gestational age include the weeks before I was pregnant?
By medical convention, pregnancy tracking begins on the first day of your last period, roughly two weeks before conception actually occurs. This is because LMP is a measurable date, whereas exact ovulation is harder to confirm without tracking.