Enter the length of the menstrual cycle and the ovulation day into the calculator to determine the length of the luteal phase. This calculator can also evaluate any of the variables given the others are known.

## Luteal Phase Formula

The following formula is used to calculate the length of the luteal phase.

LP = CD - O

Variables:

- LP is the length of the luteal phase CD is the length of the menstrual cycle O is the ovulation day

To calculate the length of the luteal phase, subtract the ovulation day from the total length of the menstrual cycle.

## What is a Luteal Phase?

The luteal phase is a stage in a woman’s menstrual cycle that occurs after ovulation and before the start of her period. It typically lasts about two weeks, during which the body prepares for a possible pregnancy. The corpus luteum, a structure that develops in the ovaries after an egg has been released, produces progesterone to thicken the lining of the uterus. If fertilization does not occur, the corpus luteum breaks down, progesterone levels drop, and menstrual bleeding begins, marking the start of a new cycle.

## How to Calculate Luteal Phase?

The following steps outline how to calculate the Length of the Luteal Phase (LP) using the formula LP = CD – O:

- First, determine the length of the menstrual cycle (CD).
- Next, determine the ovulation day (O).
- Next, subtract the ovulation day (O) from the length of the menstrual cycle (CD) using the formula LP = CD – O.
- Finally, calculate the length of the luteal phase (LP).
- After inserting the variables and calculating the result, check your answer with the calculator above.

**Example Problem:**

Use the following variables as an example problem to test your knowledge:

Length of the menstrual cycle (CD) = 28 days

Ovulation day (O) = 14