Skip to main content
🇺🇸🇪🇸🇧🇷🇫🇷🇩🇪🇨🇿
InstagramTikTok
App StoreGoogle Play

Free calculators

Phase calculator

Estimate your current menstrual cycle phase from the first day of your last period and your usual cycle length.

days
days

Your data stays on your device

The values you enter are used for calculations in your browser. These calculators do not send your entries to Lively.

Understanding the menstrual cycle

This guide describes menstruation, the follicular phase, ovulation, and the luteal phase. Menstruation is part of the follicular phase; the calculator displays it separately.

The 4 phases of your menstrual cycle

Menstruation

What's happening: Your period starts a new cycle as the uterus sheds its lining. Bleeding often lasts a few days; the length and symptoms vary.

Follicular phase

What's happening: The follicular phase begins on the first day of your period and ends at ovulation. Estrogen rises as an egg matures.

Ovulation

What's happening: Ovulation is the release of an egg from an ovary. Its timing can change from cycle to cycle, even when your periods are regular.

Luteal phase

What's happening: After releasing an egg, the follicle transforms into something called the corpus luteum, which produces progesterone to support a potential pregnancy.

  • Reed BG, Carr BR. The Normal Menstrual Cycle and the Control of Ovulation. Endotext. https://www.ncbi.nlm.nih.gov/books/NBK279054/
  • NICHD. Menstruation and Menstrual Problems. https://www.nichd.nih.gov/health/topics/factsheets/menstruation

Frequently asked questions

Progesterone is the dominant hormone during the luteal phase. After ovulation, the corpus luteum (the remnant of the follicle that released the egg) produces high levels of progesterone to prepare and maintain the uterine lining for potential pregnancy. Progesterone is responsible for many premenstrual symptoms like bloating, breast tenderness, and mood changes. If pregnancy doesn't occur, progesterone levels drop sharply, triggering menstruation.

Phase lengths vary. The follicular phase runs from the first day of bleeding to ovulation and includes menstruation. The luteal phase follows ovulation and lasts until the next period, often around two weeks.

While unlikely, it is possible to get pregnant during your period, especially if you have a shorter menstrual cycle or longer periods. Sperm can survive in your body for up to 5 days, so if you ovulate shortly after your period ends, sperm from intercourse during menstruation could still be viable. This is more common in women with 21-24 day cycles where ovulation occurs earlier. If you're not trying to conceive, it's important to use contraception throughout your entire cycle.

Important notice

This calculator gives general estimates for learning about your cycle or pregnancy. It cannot diagnose a condition or replace medical care.

Discuss health questions and results with your healthcare provider. Do not delay care because of a calculator result.

Cycle timing and pregnancy development vary. Your results may differ from these estimates.