These calculators use the same conventions as antenatal clinics: pregnancy dated from the last menstrual period with Naegele's 280-day rule (cycle-length adjusted), weeks counted the clinical way, and weight-gain guidance from the IOM ranges by pre-pregnancy BMI. They align with what your midwife's wheel or app will say.
Only about one baby in twenty arrives on the due date; the estimate is the centre of a spread, with most births landing within two weeks either side. Ultrasound dating from the first trimester can shift the calendar estimate and takes precedence when it differs — your clinic's date is the official one.
The kick counter and contraction timer are the two tools most used in late pregnancy: counting movements the standard count-to-10 way, and timing contractions with the 5-1-1 pattern that hospitals ask about. Both are aids to a conversation with your midwife, never a substitute for calling when something feels wrong.
Everything here is general information built on published guidance. Pregnancy care is individual — conditions, histories and local protocols differ — so every calculator carries the same footer in spirit: your midwife, doctor or maternity unit outranks any calculator, always.