Estimated due date (Naegele’s rule)
Pick what you know: the first day of your last period, the conception date or the age measured at a scan. The tool gives an estimated date and the usual window for birth.
General information, not medical advice. This result does not replace a doctor. If in doubt or if you have symptoms, see a health professional.
Result
October 19, 2026Estimated due date (40 weeks)
- Birth usually between September 28, 2026 (37 weeks) and November 2, 2026 (42 weeks).
- Estimated conception
- January 26, 2026
- Only a small share of babies (around 4 to 5%) are born on the estimated date itself: it is a marker, not an appointment.
Inputs
- I know
- Last period
- Date
- 2026-01-10
- Usual cycle length
- 30
How it is calculated
Naegele’s rule: first day of the last period + 280 days, moved by (cycle − 28) days when the cycle is not 28 days.
Result
Estimated due date (40 weeks)
- Estimated conception
- January 26, 2026
How it is calculated
- Naegele’s rule: first day of the last period + 280 days, moved by (cycle − 28) days when the cycle is not 28 days.
- From conception: conception + 266 days. From a scan: date − measured age + 280 days.
- Term birth window: 37 to 42 weeks.
Example
Period on 10 January 2026, 30-day cycle: estimated due date 19 October 2026, birth usually between 28 September and 2 November 2026, conception around 26 January 2026.
Good to know
- Real uncertainty: the exact date is not known in advance. The date set by your care team (often at the first-trimester scan) comes first.
- Irregular cycles, recent contraception or assisted reproduction change the calculation.
- Ask a midwife or doctor any question about the pregnancy.
Sources
- ACOG Committee Opinion 700, Methods for estimating the due date, 2017
- NICE guideline NG201, Antenatal care, 2021
When to use it
- Estimate a due date from the information you have.
- See the usual birth window without treating one estimated day as certain.
Frequently asked questions
Will the baby arrive exactly on the due date?
Not necessarily. Few babies are born on the estimated date itself; it is a guide, not an appointment.
Which dating should I follow?
Follow the date set by your care team, often confirmed with a first-trimester ultrasound.
Does cycle length change the calculation?
Yes. When counting from the last period, the estimate is adjusted if the usual cycle differs from 28 days.