Ovulation Calculator

Last Updated on January 5, 2024 by Emma

The Ovulation Calculator estimates the most probable ovulation/fertile window as well as other related dates. The estimations are based on a woman’s last period date. This calculator should not be used as a form of birth control.


Important dates for the next 6 cycles:

Related: Pregnancy Calculator

When Does Ovulation Occur?

Ovulation in humans is when ovarian follicles release one or more mature eggs from the ovaries. On average, it happens within 4 days before or after the midpoint of a woman’s menstrual cycle (14 days before her next period starts).

Days 10-18 of the cycle are usually the most fertile days. This matters for trying to get pregnant because the egg can only be fertilized for 12-24 hours after release. Since sperm can survive inside a woman for up to 5 days, having regular sex 5 days before and on the day of ovulation can increase the chances of getting pregnant. If fertilized, the egg implants in the uterus 6-12 days later. Otherwise, the next period starts, expelling blood and tissue from the uterus lining.

Predicting Ovulation

Many people want to predict their ovulation date, mostly to improve their chances of conception. Here are some common ways to estimate ovulation timing:

Menstrual Cycle Tracking

This calculator predicts ovulation by tracking menstrual cycles. Since days 10-18 are typically the fertile window, women with regular cycles can fairly easily figure out when they ovulate. But cycles vary in length, so tracking is needed to determine ovulation if you don’t have a 28-day cycle.

Cycle day 1 is when bleeding starts. Tracking periods over time shows whether they’re regular. Irregular cycles make estimating ovulation trickier.

Basal Body Temperature

Basal body temperature (BBT) is your lowest temperature when first waking up. BBT reaches its lowest point right before ovulation, then rises about 1⁄2 degree daily during ovulation. Tracking BBT for a few months can reveal ovulation patterns. But having a cold or infection can affect BBT readings.

Ovulation Test Kits

Over-the-counter ovulation tests check for hormone surges 24-48 hours before ovulation. While 99% accurate for those hormones, they can’t guarantee exactly when ovulation will happen in that time frame. These tests often track luteinizing hormone (LH) levels. High LH triggers ovulation under certain conditions.

Some kits track estrogen in saliva or sweat salts, which change earlier in the cycle. So they can predict ovulation sooner than LH tests. But they require tracking baseline levels first.

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