Period Calculator

Table of contents:
This period and ovulation tracker is a tool for tracking the feminine cycle. Given that the current world population is 7.5 billion people, roughly just more than half of them female, there's about 3.8 billion people who can make good use of this calculator. Inputs include:

•	Cycle duration - Typically 28 days for most women. If in doubt, call it 28.
•	Period duration - The number of days your period lasts. Put in the average duration. Most women have a period lasting between three and seven days.
•	Last period started - Be sure to put the day it started, not the day it ended.

The outputs will tell you the date of your next period, from first to last day. It also tells you your fertility window for ovulation, in case you're trying to conceive.

Some News About Birds And The Bees

As many of you should know if you grew up in a state with a good sex education curriculum, your peak ovulation window is just about exactly two weeks around from the start of your period.

The chances for conception here are at their best. Sperm is usually capable of living in your system for about five days maximum, although there's a variety of factors that can shorten that duration. These factors include the PH balance of your uterine mucus, or if you were recently taking contraceptives, for instance.

So the peak time to conceive is anywhere roughly from a few days after the end of your last period (accounting for hardy surviving sperm), to about two days after peak ovulation. The last week before your period has the lowest odds of conceiving. 

You should also know that the sudden absence of a period means that you might be expecting. So you can also use this tracker to check when your period is scheduled.

Every Woman Is Different

The major caveat to take away is that biology, being a natural process, is messy and imprecise. Every woman's body is different, so variations on all of the above can occur. It's rare to have a shorter or longer cycle, or just skip a period once in a while, or ovulate sooner than expected, but it does happen.

The human race has gone on for some 4.5 million years, and some of it doubtless has happened when the mother was thinking, "There's no way I can get pregnant now."

In addition, various factors can impact both your period and your fertility, including the recent use of contraception, stress, weight gain or weight loss, hormonal conditions, use of tobacco or alcohol, or prescription medications. Your reproductive system is the product of 4.5 million years of evolution bent on the best chance for survival of the species, so conditions of extreme stress can impact your conception chances when your reproductive system "decides" now isn't a good time to have a baby.

Check with your OB/GYN to help nail down the specifics of your cycle, and any irregularities you might have.

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