Find your fertile window, ovulation day, and the best days to conceive. Evidence-based tools reviewed against ACOG and ASRM fertility guidelines.
Trying to conceive — or just understanding your cycle better — starts with knowing when you ovulate. Our ovulation calculators pinpoint your fertile window, predict your most fertile days, and forecast future cycles, all free and with your data staying private in your browser.
Find your fertile window, ovulation day, and most fertile days. Includes a fertility calendar, 3-cycle forecast, pregnancy test date, and due date if you conceive.
Most PopularOnce you conceive, calculate your due date with LMP, conception, or IVF methods — plus weekly milestones and appointment timeline.
RelatedThe window for conception each cycle is surprisingly narrow — about 6 days. Miss it, and you wait another month. Hit it, and you maximize your chance of conceiving. An ovulation calculator removes the guesswork by predicting exactly when your fertile window opens and when ovulation is most likely, based on your unique cycle.
Beyond conception, understanding your cycle helps you recognize what's normal for your body, track irregularities worth discussing with a doctor, and plan around your most fertile times. Our calculator goes further than most by letting you adjust your luteal phase length — the single biggest factor that generic "day 14" calculators get wrong.
| Cycle Length | Ovulation Day | Fertile Window |
|---|---|---|
| 24 days | Day 10 | Days 5-10 |
| 26 days | Day 12 | Days 7-12 |
| 28 days | Day 14 | Days 9-14 |
| 30 days | Day 16 | Days 11-16 |
| 32 days | Day 18 | Days 13-18 |
| 35 days | Day 21 | Days 16-21 |
These assume a 14-day luteal phase. For your personalized window, use our Ovulation Calculator.
Yes, completely free with no signup. All calculations run in your browser, and no personal cycle data is stored or transmitted anywhere.
No. Calendar-based ovulation prediction is not reliable for preventing pregnancy because ovulation timing can shift unexpectedly. If you're avoiding pregnancy, use a proven contraceptive method and consult your healthcare provider.
For people with regular cycles, calendar-based calculators are typically accurate within 1-2 days. Accuracy drops for irregular cycles. For best results, combine the calculator with ovulation predictor kits (OPKs) or basal body temperature tracking.
Tracking basal body temperature or using ovulation predictor kits reflects your own cycle rather than an average. Calendar prediction assumes regularity that not everyone has, which is also why it is not a reliable method of contraception. Speak to a healthcare provider about options suited to your situation.
Get your ovulation day, fertile window, and conception forecast in under a minute. Free and instant.
Open Ovulation Calculator →Ovulation typically occurs around fourteen days before the next period begins, not fourteen days after the last one started. This distinction matters for anyone whose cycle is not exactly twenty-eight days, because the luteal phase after ovulation is relatively consistent while the phase before it varies.
The fertile window spans roughly six days: the five days before ovulation and the day itself. Sperm can survive several days in the reproductive tract, which is why intercourse before ovulation can result in conception.
| Cycle Phase | Approximate Timing | What Happens |
|---|---|---|
| Menstrual | Days 1 to 5 | Period; cycle day 1 is the first day of bleeding |
| Follicular | Days 1 to 13 | Follicles develop; length varies most between people |
| Ovulation | Around day 14 | Egg released; roughly 14 days before next period |
| Luteal | Days 15 to 28 | More consistent in length, typically 12 to 16 days |
Calendar-based prediction assumes regular cycles and consistent ovulation timing, neither of which holds for everyone. It is not a reliable method of contraception. For preventing pregnancy, speak to a healthcare provider about appropriate methods.