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Ovulation Calculator for a 30-Day Cycle

Estimate your ovulation date, fertile days, and next period from your last period and cycle length.

Estimated ovulation date

Forecast for the next 3 cycles

This is an approximate calculation for general orientation, not medical advice. Cycles naturally vary — please consult your doctor for contraception or fertility guidance.

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Result

This page opens the ovulation calculator with a 30-day cycle preselected — add the first day of your last period and the fertile days appear instantly. With 30 days between periods, ovulation is estimated around day 16 (30 minus the 14-day luteal phase), and the fertile window spans days 11 through 16.

A 30-day cycle is completely within the normal range and simply means the first, follicular phase of your cycle takes a couple of days longer than in the textbook 28-day example. The second half — the luteal phase — stays close to 14 days for most women regardless of cycle length, which is exactly why the calculator counts backwards from the expected next period.

Check the forecast table for the three cycles ahead to plan further than one month. Everything is computed locally in your browser and nothing is stored. The result is an approximate guide, not medical advice — cycle tracking apps, ovulation tests, and your doctor can refine it.

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Accepted Formats & Rules

  • Ovulation estimate: cycle length minus 14 days.
  • Fertile window: 5 days before ovulation plus the ovulation day.
  • Forecast table for the next 3 cycles.

Key Benefits

✓ Shows the full picture at once: ovulation date, six fertile days, next period, and a forecast for the three following cycles.
✓ Adapts to your body: any cycle length from 21 to 35 days, using the standard 14-day luteal phase.
✓ Completely private: dates are calculated in your browser and never leave your device.

Use Cases

  • • Find your estimated ovulation date and 6-day fertile window from the last period and cycle length.
  • • See when the next period is expected and plan ahead with a forecast for the next 3 cycles.
  • • Compare short (21-day) and long (35-day) cycles to understand how the fertile days shift.