How big will they be?
Birth weight is mostly genetics, gestational age, and how the pregnancy went — not magic. Here's an honest range based on the factors that actually move the number.
Birth weight prediction is, honestly, more art than science. We're using a regression that captures the biggest factors — gestational age, parental size, parity, sex — but the ±1 lb range exists because we genuinely cannot do better from the inputs you can give us in a form.
Tall parents, gestational diabetes, placental insufficiency, fetal growth restriction, and a dozen other things your OB tracks can shift the actual number meaningfully. Treat the prediction as a midpoint with wide uncertainty, not a target.
Their name, birth date, time, weight, and length on cream matte paper. Hangs in the nursery, ages well.
Free, attribution-only. One iframe — your readers stay on your page, the calculator works exactly the same, and the math runs on willthey.baby so we keep it accurate.