Due date calculators help estimate a likely delivery date from standard pregnancy timing inputs such as last menstrual period, conception date, IVF transfer date, or ultrasound-based information.
They are useful for awareness and planning, but they do not replace prenatal care or clinician-confirmed dating.
Why Different Input Methods Exist
Different pregnancies start with different known information. Some people know the last menstrual period, some know conception or transfer timing more clearly, and some rely more on ultrasound dating.
Why the Estimate Can Change
A due date estimate can shift when cycle timing is uncertain, when later clinical information is more reliable, or when the original dating assumption was only approximate.
What a Calculator Is Good For
A calculator is useful for milestone awareness and general planning. It is not suitable for medical decision-making when official prenatal records or clinician guidance are available.