Ovulation Calculator

The first day of proper bleeding, not spotting the day before. That day is cycle day 1, and every date in the result is counted from it. Using a spotting day instead shifts the whole estimate by a day or two.

Enter your typical length, then read the window as wider than it looks. A cycle that swings between 26 and 32 days moves ovulation across roughly six days, so run the calculation for your shortest and your longest cycle and treat everything between the two fertile windows as possible.

It is an estimate of the average case. Studies of cycle tracking find that ovulation falls outside the predicted window in a large minority of cycles, even for people with regular periods. Ovulation tests (LH), basal temperature, or cervical mucus observations narrow it down far better because they measure what is actually happening this month.

No. Treating "outside the fertile window" as safe is unreliable, because the window itself is only an estimate and sperm survival stretches the risk earlier than most people assume. Use an actual contraceptive method; a calendar is not one.

Because the two cells have very different lifespans. Sperm can wait several days in the reproductive tract for an egg; an egg is fertilisable for about a day after release. Intercourse before ovulation therefore has a much longer reach than intercourse after it.

It is the number of days from ovulation to the start of the next period, typically 12 to 14 and fairly constant for one person. You learn it by tracking: a positive ovulation test or a sustained temperature rise marks ovulation, and the days from there to your next period are your luteal phase. If you have never measured it, 14 is a reasonable default.

The two or three days immediately before ovulation and ovulation day itself carry the highest chance. Every other day across the fertile window is a common approach, since it keeps sperm present without requiring precise timing you cannot actually verify in advance.

Realistically from the day the period is due, which is about 14 days after ovulation. The implantation window shown in the results (6–12 days after ovulation) is when hCG starts to appear, but levels are usually too low to detect until near the end of it — testing earlier mostly yields false negatives.

A luteal phase shorter than about 10 days shortens the whole cycle. It can be normal variation, but a persistently short luteal phase is worth mentioning to a doctor. Try re-running the calculation with your actual luteal length to see how much the fertile window moves.

The arithmetic works, but the input does not mean much yet. Cycles after stopping the pill are often irregular for a few months, so any single cycle length is a poor predictor. Track two or three natural cycles first, then use your median length.

Because most add 280 days to the last period regardless of cycle length. This tool adds 266 days to the estimated ovulation date, which is the same thing for a 28-day cycle but more consistent for longer or shorter ones. Either way, a first-trimester ultrasound is what a clinic will actually date the pregnancy from.

Completely. There is no account, no storage and no upload: the dates exist only in the page while it is open, and analytics never receives them. Reload and the tool forgets everything.