Conception Date Calculator
Free conception calculator and conception date calculator to explore when you may have conceived—as an estimate only, never a guaranteed exact date.
Pregnancy calculators and fetal growth reference tools for educational use.
Plain-language interpretation
Sperm can survive several days and ovulation timing varies. Even when the math returns a single calendar day, treat it as the center of a probable window—not proof of a specific act or fertilization moment.
Formula and dating standard
- From EDD: conception ≈ EDD − 266 days
- From LMP: conception ≈ LMP + 14 days (28-day cycle assumption)
- From assessment + gestational age: imply LMP, then conception ≈ LMP + 14 days
Important assumptions
- Cannot confirm exact intercourse, fertilization, or parentage.
- Does not promise an “exact conception date.”
- LMP path assumes mid-cycle ovulation.
Applicable use
Educational estimates during pregnancy when EDD, LMP, or a known gestational age is available. Not for legal, forensic, or paternity determination.
Worked example
EDD 2024-10-07 → estimated conception 2024-01-15 (266 days earlier). A ±3-day educational window spans 2024-01-12 to 2024-01-18.
Limitations
- Not diagnostic and not a paternity tool.
- Ultrasound-adjusted clinical dating may shift the estimate.
- ART conceptions should use transfer and embryo-age information.
Frequently asked questions
- Can this tool give an exact conception date?
- No. It estimates a probable conception date and a short educational window. It cannot confirm the exact day of intercourse, fertilization, or parentage.
- How is conception estimated from a due date?
- Estimated conception date = estimated due date minus 266 days, reflecting a common 38-week interval from conception to EDD in educational dating.
- What if I only know how many weeks pregnant I am?
- Use the gestational-age mode: the tool backs out an implied LMP from assessment date and known weeks+days, then places conception near LMP + 14 days.
Last content review: 2026-07-18. Formula version: pregnancy-dates-v1.