Ovulation Calculator for a 30-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 30-day cycle preselected — add the first day of your last period and the fertile days appear instantly. With 30 days between periods, ovulation is estimated around day 16 (30 minus the 14-day luteal phase), and the fertile window spans days 11 through 16.
A 30-day cycle is completely within the normal range and simply means the first, follicular phase of your cycle takes a couple of days longer than in the textbook 28-day example. The second half — the luteal phase — stays close to 14 days for most women regardless of cycle length, which is exactly why the calculator counts backwards from the expected next period.
Check the forecast table for the three cycles ahead to plan further than one month. Everything is computed locally in your browser and nothing is stored. The result is an approximate guide, not medical advice — cycle tracking apps, ovulation tests, and your doctor can refine it.
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.