Pregnancy
Estimated conception
Assumes ovulation on day 14 of a 28 day cycle. Conception therefore falls about two weeks after the count begins.
The Formula
conception = LMP + 14 days
Assumes ovulation on day 14 of a 28 day cycle. Conception therefore falls about two weeks after the count begins.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| LMP | Last menstrual period | date | First day of bleeding. |
| 14 | Days | days | Typical ovulation day in a 28 day cycle. |
| C | Conception | date | Estimated fertilisation date. |
What Each Symbol Means
LMPdate
Last menstrual period
First day of bleeding.
14days
Days
Typical ovulation day in a 28 day cycle.
Cdate
Conception
Estimated fertilisation date.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate a due date page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate A Due Date, filed under Health. Every number the guide produces comes from substituting into this one line.