Pregnancy
Estimated ovulation day
Counts back the luteal phase from the next expected period.
The Formula
O = C - P
Counts back the luteal phase from the next expected period.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| O | Ovulation day | days | Counted from the first day of bleeding. |
| C | Cycle length | days | The total length of the cycle. |
| P | Luteal phase | days | The interval from ovulation to the next period. |
What Each Symbol Means
Odays
Ovulation day
Counted from the first day of bleeding.
Cdays
Cycle length
The total length of the cycle.
Pdays
Luteal phase
The interval from ovulation to the next period.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate ovulation 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 Ovulation, filed under Health. Every number the guide produces comes from substituting into this one line.