Ovulation Calculator for a 28-Day Cycle
Estimate your ovulation date, fertile days, and next period from your last period and cycle length.
Processed entirely in your browser — nothing you enter here is ever uploaded.
Result
About this tool
This page opens the ovulation calculator with a 28-day cycle already set — just enter the first day of your last period to see your estimated ovulation date and fertile days. The 28-day cycle is the textbook reference: with a 14-day luteal phase, ovulation lands right in the middle, on day 14, and the fertile window covers days 9 through 14.
In reality only a minority of women have a precise 28-day rhythm every month — studies show most cycles fall between 25 and 31 days and vary a little from month to month. So even with a "standard" cycle it is worth treating day 14 as the center of a range rather than a guarantee, and paying attention to your body’s signals such as cervical mucus changes or ovulation test strips.
Enter the date and read the forecast for this cycle and the next three — including when each period is expected. The calculation never leaves your browser. It is an estimate for orientation, not medical advice or a contraception method.
Example. A last period on 1 January 2024 and a 28 day cycle returns ovulation on 14 January, a fertile window from 9 January through 14 January, and the next period on 29 January.
Limit. Cycle length is accepted only from 21 to 35 days, and ovulation is always placed by subtracting a fixed 14 day luteal phase.