Summary
Calendar estimate of ovulation and fertile window from cycle assumptions.
Calculation details
Calendar-safe UTC arithmetic preserves date-only values. Actual ovulation and cycle length can vary even when averages are regular.
Formula
Next period = cycle start + cycle length; ovulation = next period - luteal phase; fertile window = ovulation - 5 days through ovulation + 1 day.
Worked example
Ovulation worked example
A regular 28-day cycle with a 14-day luteal phase estimates ovulation near cycle day 14.
How it works
Enter the last period start, average cycle length, and luteal-phase assumption. Cycles vary — this is not contraception and does not confirm ovulation.
Frequently asked questions
Is this a medical diagnosis?
No. It is an educational estimate and cannot diagnose a condition or replace individualized professional advice.
Why can my actual result differ?
Ovulation timing varies even in regular cycles; calendar methods do not confirm ovulation.
When is this calculator most useful?
Use it to sketch a fertile window for education — not for contraception or fertility treatment.
How are results rounded?
The calculation retains full precision; centralized display formatting rounds only the visible result.