How the due date is calculated
The estimated due date uses Naegele's rule: 280 days (40 weeks) from the first day of your last period, adjusted for your cycle length (ovulating later shifts the date later). Only about 1 in 20 babies arrives on the exact date — most come within two weeks either side — and a first-trimester dating ultrasound is more accurate than any calendar method and will refine this estimate.
The standard checkup schedule
The visit plan the tool shows follows the widely used antenatal pattern: a booking visit at 8–12 weeks (blood tests, history, folic acid check), dating & screening scan at 11–14 weeks, the detailed anomaly scan at 18–22 weeks, glucose screening at 24–28 weeks (gestational diabetes), plus blood pressure and growth checks that become more frequent from 28 weeks — typically every 4 weeks, then every 2 from 36, then weekly at term. Your own doctor may adjust this; higher-risk pregnancies get more visits, and that plan always wins over any calculator.
Warning signs at any stage
Bleeding, severe abdominal pain, severe headache with vision changes, sudden swelling of face/hands, fever, fluid leakage, or a clear drop in the baby's movements after 28 weeks — these are same-day medical calls, not wait-for-the-next-appointment items.
Practical guide for using this result
How the due date is estimated
Last-menstrual-period dating assumes a typical cycle; first-trimester ultrasound may revise the date when measurements differ.
Milestones are windows
Screening and checkups occur across date ranges, and local schedules vary by country and individual risk.
Using the tool safely
Use it to prepare questions and dates, not to delay care or interpret urgent symptoms.
How to use an estimated due date and timeline
A due date is a planning estimate, not an appointment the baby must keep. Early ultrasound and clinical history may revise the date.
Use the dating method consistently
Last-menstrual-period dating assumes a typical cycle and known first day. Conception or embryo-transfer dates can be more specific when accurately known.
Treat milestones as windows
Screening and check-up timing varies by country, medical history and clinician. Use the timeline to prepare questions, then follow the care team’s schedule.
Seek care for urgent symptoms
Heavy bleeding, severe abdominal pain, fainting, severe headache, reduced fetal movement later in pregnancy or fluid leakage need prompt medical advice.
Sources & references
- ACOG. Methods for estimating the due date. Committee Opinion No. 700. 2017.
- WHO recommendations on antenatal care for a positive pregnancy experience. 2016.
- NHS. Your antenatal appointment schedule.