Ovulation Calculator
Two quick details, tuned to your cycle instead of a generic 28-day average. Out comes your fertile window, your most fertile day, and when your next period's due. No sign-up, no data leaves your browser.
31 Jul – 6 Aug
Upcoming fertile windows
Sperm can survive about five days and the egg lasts around a day, so the run-up to ovulation counts as much as the day itself. These are estimates from your average cycle, not a substitute for a test or a doctor.
Know your window without the guesswork.
Bleed learns your real cycle and predicts your fertile window on its own — free, no account required, all on your phone.
What this ovulation calculator does
Two quick details and it does the rest: the first day of your last period and your usual cycle length. That's all a free ovulation calculator needs to work out when you're likely to ovulate, the fertile days on either side of it, and when your next period should turn up — not just for one cycle, but across the ones ahead.
Most tools give you a single date and leave it there. This one lays your fertile window out day by day, marks your most fertile day, and stacks the next few windows behind it — more like an ovulation calendar calculator you can plan around than a one-off guess. If the single date is all you came for, it's called out as your most fertile day, right under the window, as a plain ovulation date calculator.
Because everything keys off your cycle length, it also works as an ovulation cycle calculator. Nudge the cycle slider and every date moves with it. Short cycle, long cycle, whatever yours does, the maths follows.
How this is calculated
The luteal phase — the stretch between ovulation and your next period — is remarkably consistent at around 14 days for most people. So we work backwards: ovulation lands roughly 14 days before your next period starts.
On a 28-day cycle that puts ovulation around day 14. On a 32-day cycle it's day 18; on a 24-day cycle, day 10. The fertile window is the five days before ovulation plus the day of and the day after — sperm can hang around for several days, so the run-up matters more than the day itself.
These are the exact calculations the Bleed app uses. The difference: the app learns your real cycle from what you log and adapts over time. This calculator uses the average you give it.
Your data stays yours
Everything here runs in your browser. Nothing you type is sent to a server, logged, or sold. Close the tab and it's gone. Same principle as the app.
It's an estimate
A calculator can point at the likely days — it can't diagnose anything or work as birth control. Cycles shift with stress, illness, and life. For anything medical, see a professional.
Common questions
- Is this ovulation calculator free?
- Yes. No account, no paywall, no upsell. The ovulation calculator is free, and it stays that way. We don't even keep what you type. It runs in your browser and disappears when you close the tab.
- How accurate is an ovulation date calculator?
- It's an estimate, not a promise. An ovulation date calculator assumes your cycles are fairly regular and that ovulation happens about 14 days before your period. Real bodies drift with stress, sleep, illness, and age, so treat the dates as a solid guess rather than a guarantee.
- Can I use it to avoid or plan a pregnancy?
- Use it to understand your cycle, not as birth control. The fertile window is wider and messier than any calculator can capture. If you're trying to conceive or avoid it, talk to a doctor about methods that track ovulation directly, like temperature or LH tests.
- What if my cycle is irregular?
- It still works as an ovulation cycle calculator, but the more your cycle length swings month to month, the less any single prediction can tell you. If yours are all over the place, logging a few months in an app will beat a one-off calculation.
Want it to learn your actual cycle?
Bleed tracks what you log and predicts your ovulation and period on its own — all on your phone.
iOS only. Your data never leaves your phone.