What the tool does, how to run it, and what to expect from the result.
Enter the first day of your last period and your usual cycle length. The next period is that date plus one cycle; ovulation is estimated 14 days before the next period, and the fertile window spans the five days before ovulation through the day after. Irregular cycles move these dates, so average a few recent cycles for the best estimate. It is a planning aid, not contraception or medical advice.
A quick way to understand who this helps, what it solves, and where it connects next.
People tracking their menstrual cycle or planning around their next period.
Using the period calculator without installing anything or signing up.
Short answers for the questions people usually have before trying a utility like this.
By adding your average cycle length to the first day of your last period. A 28-day cycle that started on March 1 points to March 29. Count cycle length from the first day of one period to the first day of the next.
Cycles vary by a few days for many people; stress, illness, travel, weight change and some medications can shift them further. A cycle that is more than a week late with a chance of pregnancy is worth a test, and repeated irregular cycles are worth raising with a doctor.
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Enter the first day of your last period and your average cycle length to estimate your fertile window, ovulation day, and next period. All calculations run in your browser.
This is an estimate for general information only and is not medical advice or a form of contraception.