Estimate of the conception period of a pregnancy
Enter the due date, or the pregnancy age given at a date (for example at a scan). The tool gives a likely conception date and an interval around it.
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
May 15, 2026Likely conception
- Estimated interval: May 8, 2026 to May 22, 2026.
- Matching due date
- February 5, 2027
- This estimate can never establish paternity. Only a legally supervised genetic test can do that.
Inputs
- I know
- The due date
- Date
- 2027-02-05
How it is calculated
From the due date: conception ≈ due date − 266 days (two weeks after the theoretical start of pregnancy, 280 days before the due date).
Result
Likely conception
- Matching due date
- February 5, 2027
How it is calculated
- From the due date: conception ≈ due date − 266 days (two weeks after the theoretical start of pregnancy, 280 days before the due date).
- From a dating: theoretical start = date − pregnancy age; conception ≈ that start + 14 days.
- The ± 7 day interval reflects the usual accuracy of a dating and the variation of the ovulation day.
Example
Due date 5 February 2027: likely conception 15 May 2026, interval 8 to 22 May 2026.
Good to know
- The day of ovulation and fertilisation varies between people and cycles; the interval is not a certainty.
- Never establishes paternity or the date of a specific intercourse.
- After assisted reproduction, the date is known by the medical team.
Sources
- ACOG Committee Opinion 700, Methods for estimating the due date, 2017
- Wilcox A.J. et al., BMJ, 2000 (ovulation variability)
When to use it
- Estimate a likely conception period from a due date or pregnancy dating; do not use it to infer paternity.
Frequently asked questions
How is the likely conception period estimated?
From a due date, the estimate counts back about 266 days. From pregnancy dating, it estimates the theoretical start of pregnancy and adds about 14 days.
Can this estimate identify a child’s father?
No. An estimated period cannot establish paternity. Genetic testing and its legal process depend on local law.
How precise is the interval shown?
Ovulation varies from cycle to cycle, and pregnancy dating has a margin of uncertainty; the ±7-day interval is only an estimate.