Ovulation Calculator for a 35-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 preset for a long 35-day cycle — enter the first day of your last period and the estimate appears immediately. With 35 days between periods, ovulation is expected around day 21, and the fertile window covers days 16 through 21 — noticeably later than the mid-cycle timing many charts assume.
Long cycles stretch the follicular phase: the egg simply takes longer to mature, while the luteal phase remains near 14 days. That is why counting "14 days after the period starts" fails for long cycles — the right anchor is 14 days before the next period. Cycles up to 35 days are considered within the normal range; consistently longer or highly irregular cycles are worth discussing with a doctor, as they can point to late ovulation or anovulatory months.
Use the three-cycle forecast to see period and fertile-day dates further ahead. The math runs entirely in your browser and stays private. Treat the result as an approximate guide, not medical advice — with long cycles, ovulation tests or ultrasound monitoring give a much more reliable picture.
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.