Ovulation Calculator — Fertile Window & Cycle Calendar
Estimate ovulation, fertile-window and next-period dates from an average cycle or a variable cycle-length range, with a visual calendar and three-cycle forecast.
Cycle and fertile-window planner
Estimate dates from your cycle history. Calendar predictions cannot confirm ovulation or provide contraception.
Current-cycle timeline
Cycle calendar
| Cycle | Estimated ovulation | Fertile window | Next period |
|---|
How the ovulation estimate works
Average-cycle mode places ovulation about 14 days before the next expected period. NHS guidance notes that ovulation often occurs roughly 10–16 days before the next period, so the range mode shows that uncertainty instead of one exact date.
What is the fertile window?
The estimate starts five days before possible ovulation and ends one day after it. The Office on Women's Health notes that sperm can live 3–5 days and an egg about 12–24 hours after ovulation.
Irregular cycles
Enter the shortest and longest recent cycle. The result deliberately widens across both cycle length and the 10–16-day pre-period ovulation range. Tracking cervical mucus, basal temperature, or an ovulation test may add information.
Planning, not diagnosis
This calculator cannot confirm whether ovulation happened, estimate a personal chance of pregnancy, diagnose irregular periods, or replace care. Seek clinical advice for cycle concerns or difficulty conceiving.
Frequently asked questions
Is an ovulation calculator exact?
No. It estimates calendar dates from cycle history, while actual ovulation can move from cycle to cycle.
Can I use these dates to avoid pregnancy?
No. A simple calendar prediction is not reliable contraception. ACOG fertility-awareness methods require specific instructions and daily observations.
Why is the range wide for variable cycles?
It includes both the shortest-to-longest cycle history and the NHS 10–16-day range before the next period.
When should I take a pregnancy test?
A missed period is a common first sign. Follow the test instructions and contact a healthcare professional when results and symptoms do not agree.
Sources
Office on Women's Health: Menstrual CycleACOG: Fertility AwarenessNHS: Periods and Fertility
