A due date is an estimate of gestational timing, not a prediction of the exact day labor will begin. Pregnancy Due Date Calculator uses the dating method available on the page—commonly the first day of the last menstrual period and the standard 280-day convention—to estimate an expected delivery date.
Cycle length, uncertain menstrual dates, assisted conception, and ultrasound findings can affect clinical dating. Normal births also occur across a range around the estimated date. Use this calculator for general planning and understanding, while prenatal care and ultrasound dating should guide medical decisions about gestational age.
How to use this tool
How does the Pregnancy Due Date Calculator work?
How to use Pregnancy Due Date Calculator
- Enter the date requested by the calculator, such as the first day of the last menstrual period when that method is used.
- Enter cycle information if the calculator provides an adjustment for cycle length.
- Calculate the estimated due date.
- Treat the result as an estimate rather than a guaranteed delivery date.
- Use prenatal care and ultrasound dating guidance from a qualified healthcare professional when clinical decisions depend on gestational age.
Clinical dating reference
The 280-day LMP convention and clinical use of ultrasound for pregnancy dating are described by ACOG – Methods for Estimating the Due Date.
Examples
LMP example
A 280-day convention gives an estimated due date around 8 October 2026, subject to clinical dating and individual variation.
Known conception date
Conception-based dating uses a different starting point than LMP dating; do not add 280 days to conception.
Irregular cycle
LMP-based dating can be less accurate because the standard convention assumes a typical ovulation pattern.
Common use cases
- Estimating an initial due date
- Understanding gestational weeks
- Preparing prenatal questions
- Planning appointment timelines
- Pregnancy education
Frequently asked questions
How is a pregnancy due date commonly estimated?
A common clinical convention estimates 280 days, or 40 weeks, from the first day of the last menstrual period when that date is reliable.
Is a calculated due date the exact delivery date?
No. It is an estimated date used to organize gestational timing. Normal delivery can occur before or after the estimated date.
What if my menstrual cycle is not 28 days?
Cycle length and the actual timing of ovulation can affect an LMP-based estimate. Some calculators allow an adjustment, while clinical dating may be revised by ultrasound.
Can ultrasound change the estimated due date?
Yes. Clinicians may use ultrasound dating and established obstetric guidance when the menstrual date is uncertain or measurements support a different estimate.
Can this calculator replace prenatal dating advice?
No. Use it for general planning and education; clinical gestational-age decisions should follow prenatal care from a qualified healthcare professional.