Ovulation Calculator Calculator

Ovulation Calculator Calculator helps estimate Korea-related pregnancy, ovulation, fetal week, due-date, and maternity planning assumptions in English.

Cycle inputs

Ovulation is calculated as next expected period minus 14 days. The fertile window is five days before ovulation through one day after ovulation.

Ovulation result

Next ovulation

2026-07-01

Fertile 2026-06-26 to 2026-07-02

Peak fertility

2026-08-26

33% model probability on day 0

Current phase

Menstrual phase

Today is outside the fertile window

Days to next period

28 days

Upcoming cycles

  • Cycle 1: ovulation 2026-07-01, fertile 2026-06-26 to 2026-07-02, test from 2026-07-15
  • Cycle 2: ovulation 2026-07-29, fertile 2026-07-24 to 2026-07-30, test from 2026-08-12
  • Cycle 3: ovulation 2026-08-26, fertile 2026-08-21 to 2026-08-27, test from 2026-09-09
  • Cycle 4: ovulation 2026-09-23, fertile 2026-09-18 to 2026-09-24, test from 2026-10-07

Related calculators

Ovulation and fertile window calculator

This English page follows the Korean ovulation calculator logic. It calculates ovulation as the next expected period minus the 14-day luteal phase, then shows fertile windows, peak days, pregnancy test date, and multiple future cycles.

Core cycle model

The Korean source uses a default luteal phase of 14 days. If the average cycle is 28 days, estimated ovulation is around cycle day 14. If the cycle is 35 days, estimated ovulation moves to around day 21. The model therefore changes with cycle length instead of using one fixed day for everyone.

The fertile window begins 5 days before ovulation and ends 1 day after ovulation. The peak fertility interval starts 2 days before ovulation and includes ovulation day. The pregnancy test date is calculated as 14 days after ovulation, close to the next expected period.

  • Default luteal phase: 14 days.
  • Recommended cycle length input range: 21 to 45 days.
  • Fertile window: ovulation minus 5 days through ovulation plus 1 day.
  • Peak window: ovulation minus 2 days through ovulation day.
  • Pregnancy test date: ovulation plus 14 days.

Conception probability table

The calculator keeps the Korean probability table around ovulation. It is a planning guide, not a guarantee. The highest model probability is on ovulation day, while the preceding two days are also important because sperm can survive for several days.

The source constants assign 4 percent at 5 days before ovulation, 8 percent at 4 days before, 14 percent at 3 days before, 27 percent at 2 days before, 31 percent at 1 day before, 33 percent on ovulation day, and 8 percent one day after ovulation.

Cycle phase summary

The Korean calculator identifies the current phase within a predicted cycle: menstrual, follicular, ovulation, or luteal. The first 5 days are treated as the menstrual phase, days before the ovulation window are follicular, ovulation day plus or minus one day is the ovulation phase, and the remaining days are luteal.

Because the calculation uses today as the reference date, the result changes automatically as time passes. Irregular cycles, postpartum cycles, hormonal contraception, and fertility medication can reduce the usefulness of a simple cycle model.

How to use the result

Use the first predicted cycle for near-term planning and the later cycles for rough schedule awareness. If cycles vary by more than several days, update the last period date and average cycle length each month rather than relying on an old saved scenario.

For medical fertility care, combine this result with clinician guidance, ovulation tests, ultrasound monitoring, or basal body temperature if appropriate. The calculator is designed to make the Korean source assumptions visible in English, not to replace a fertility evaluation.