Due Date Calculator
Estimate your pregnancy due date, current week, and trimester from your last menstrual period or conception date.
What Is a Due Date Calculator?
A due date calculator estimates when your baby is expected to arrive based on either the first day of your last menstrual period (LMP) or the date of conception. This is the same method doctors and midwives use during early prenatal visits to establish your estimated due date, also called the EDD.
The standard calculation adds 280 days (40 weeks) to the LMP date, which is known as Naegele's rule. If you know your conception date, the calculator adds 266 days (38 weeks) instead, since conception typically occurs about two weeks after the start of your period.
Keep in mind that only about 5% of babies arrive on their exact due date. Most births occur within a two-week window around the EDD, anywhere from 38 to 42 weeks. This calculator also shows your current week of pregnancy, which trimester you're in, and a progress timeline so you can track major milestones.
Frequently Asked Questions
How is a due date calculated?
A due date is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period, or 266 days (38 weeks) from the date of conception. Both methods typically give the same estimated due date because conception generally occurs about 14 days after the start of the last period.
How accurate is a due date calculator?
Due date calculators provide a good estimate, but they're not exact. Only about 5% of babies are born on their due date. Most arrive within two weeks before or after, between weeks 38 and 42. An early ultrasound (weeks 8-12) can refine the estimate further.
What are the three trimesters of pregnancy?
The first trimester covers weeks 1 through 12 and involves rapid early development. The second trimester spans weeks 13 through 26, when many parents learn the baby's sex and feel the first kicks. The third trimester runs from week 27 until delivery, a period of significant growth and preparation.
Can my due date change?
Yes. An early ultrasound may adjust your due date if the baby's measurements differ from the LMP-based estimate by more than a week. The ultrasound-based date is generally considered more accurate, especially if your menstrual cycle is irregular.
What is the difference between gestational age and fetal age?
Gestational age is counted from the first day of the last menstrual period, which is about two weeks before conception actually occurs. Fetal age counts from the actual conception date. Doctors use gestational age as the standard, so when they say you're "8 weeks pregnant," the embryo is actually about 6 weeks old.
Example Calculation
A woman's last menstrual period started on January 15, 2025. Using Naegele's rule:
- LMP: January 15, 2025
- Add 280 days (40 weeks)
- Estimated due date: October 22, 2025
- Estimated conception: around January 29, 2025 (day 14 of cycle)
If she checks on April 15, 2025, she would be 13 weeks pregnant (into the second trimester) with about 190 days remaining until her due date.
This same result can be reached by entering the conception date of January 29 and adding 266 days, which also lands on October 22, 2025.