Ovulation Calculator
Free ovulation calculator: your fertile window, estimated ovulation day and next three cycles from your last period and cycle length. Private, in-browser.
updated
- ✓ Runs in your browser — nothing uploaded
- ✓ No sign-up
- ✓ Free, no limits
This ovulation calculator maps your fertile days from two inputs: the first day of your last period and your average cycle length. It returns your estimated ovulation day, the fertile window around it, your next period, and the same dates for the following two cycles, so you can plan a whole quarter at a glance.
The method is the standard calendar one: ovulation happens about 14 days before the next period starts — so cycle length minus 14 days after the LMP — and the fertile window is the five days before ovulation plus ovulation day itself, the six days ACOG identifies, because sperm survive up to five days while the egg lasts about one.
Calendar estimates fit regular cycles; if yours vary by more than a few days, ovulation-predictor kits or temperature tracking read your body rather than the calendar and will beat any date arithmetic. And the fertile window is a conception-planning tool, not contraception — the other days are not 'safe days'. Nothing you enter is uploaded; the dates are computed in your browser.
Frequently asked questions
When do I ovulate?
Typically about 14 days before your next period — not 14 days after the last one, unless your cycle is exactly 28 days. With a 32-day cycle, ovulation lands around day 18.
What are the best days to conceive?
The five days before ovulation plus ovulation day. The two or three days immediately before ovulation carry the highest probability, because sperm are already in place when the egg is released.
Can I use this as contraception?
No. Calendar math has real error bars — cycles shift with stress, illness and age, and sperm survive for days. Fertility-awareness contraception needs symptom tracking and instruction, not a calculator.
What if my cycles are irregular?
The estimate degrades with irregularity. Enter your average, treat the window as approximate, and consider ovulation test strips (LH kits) — they detect the hormone surge a day or so before ovulation actually happens.