Due Date Calculator – Pregnancy Due Date

How to use the calculator

1. In First day of your last menstrual period (LMP), enter the date your most recent period began—not the date it ended. Use the date before the pregnancy, even if you later had spotting.
2. In Cycle Length, select the number of days in your usual menstrual cycle, counted from the first day of one period to the first day of the next. The available choices are 20 to 45 days.
3. Read Pregnancy Conception Date for the estimated date of conception and Expected Date of Delivery for your estimated due date.

If you are unsure of your cycle length, 28 days is a common starting assumption. Select 28 from the list rather than assuming it is already selected, and remember that an uncertain cycle length makes both estimates less precise.

What your pregnancy due date means

A pregnancy due date is an estimate, not a scheduled birth date. Pregnancy is conventionally dated from the first day of the last menstrual period, which is usually about two weeks before ovulation in a 28-day cycle. On that basis, 40 weeks of pregnancy equals 280 days from the LMP. Changing the cycle length shifts the estimated ovulation date and due date by the same number of days.

The Pregnancy Conception Date result estimates when ovulation—and possible fertilization—occurred. It cannot identify the exact day conception happened. Ovulation may vary from cycle to cycle, and sperm can survive for several days before fertilization. The result is best read as a calendar estimate rather than confirmation of when pregnancy began.

The Expected Date of Delivery provides a reference point for prenatal care and for interpreting how far along a pregnancy is. Many babies are born before or after their due date. If you want to follow the timeline in weeks and days, use the Gestational Age Calculator or How Many Weeks Pregnant Are You? calculator.

Assumptions and practical limitations

The calculation assumes a fairly regular cycle and ovulation approximately 14 days before the next period. A longer selected cycle produces a later estimated conception date and due date; a shorter cycle produces earlier dates. Cycle length alone cannot reveal when ovulation actually happened, particularly if your periods are irregular.

LMP-based dating may be less reliable if you do not know when your last period began, recently stopped hormonal contraception, have irregular bleeding, or conceived soon after a previous pregnancy. Bleeding in early pregnancy can also be mistaken for a period. If any of these apply, tell your healthcare professional what you know about your dates instead of relying on the calculator result alone.

An early pregnancy ultrasound can help establish gestational age, especially when menstrual dates are uncertain. Its estimate may differ from this calculator’s result. A healthcare professional can decide which due date to use for your medical record; do not change a date they have established solely because a later calculation differs. For an ultrasound-based estimate, see the Ultrasound Gestation Period calculator.

Using your estimate

Keep the LMP date, selected cycle length, and calculated due date together so you can explain how you arrived at the estimate during a prenatal visit. If you later learn that your usual cycle length differs from the value you entered, recalculate and discuss any meaningful difference with your healthcare professional.

If you are comparing dates after fertility tracking, keep in mind that an estimated ovulation day and a known date of intercourse are not necessarily the same as the day of fertilization. The Date of Conception calculator offers another way to explore conception timing. Neither estimate replaces clinical dating or confirms paternity.