Due date estimates
Many due date calculators start from the last menstrual period and a typical gestational length. Conception-date and cycle-length options can refine the estimate, but ultrasound and clinical context may change dating.
Ovulation windows
Ovulation calculators often estimate ovulation as occurring before the next expected period. Real cycles vary, so the result should be presented as a window, not a guarantee.
Weight gain estimates
Pregnancy weight gain ranges depend on pre-pregnancy BMI category, number of fetuses and clinical context. These calculators require especially clear limitations.
Useful calculators
- Pregnancy Due Date Calculator
- Ovulation Calculator
- Pregnancy Weight Gain Calculator
- Pregnancy and Cycle Formulas
FAQ
Is a due date exact?
No. It is an estimate, and many births occur before or after the estimated date.
Can cycle calculators confirm pregnancy or fertility?
No. They estimate timing only.
When should medical advice be used?
For pregnancy symptoms, clinical decisions, unusual cycles or health concerns, use qualified medical care.
References
- ACOG: fetal growth during pregnancy, accessed 2026-05-14.
Named methods
Pregnancy calculators commonly use last menstrual period, conception date, cycle length and sometimes current gestational age. The common LMP method adds 280 days from the first day of the last menstrual period, assuming a 28-day cycle.
Concrete scenario
With an LMP date of January 1 and a 28-day cycle, the simple 280-day estimate gives an early October due date. If the average cycle is 35 days, ovulation may have occurred later and the estimate can shift.
Medical caveats
Ultrasound dating can revise estimates.
Irregular cycles reduce reliability.
Assisted reproduction has its own dating rules.
Bleeding, pain or pregnancy concerns should be handled by clinical care, not a calculator.
Last reviewed: 2026-05-14.