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Calcimator

Ovulation Calculator

Estimate your ovulation date and fertile window based on cycle length and last menstrual period. Plan or prevent pregnancy with cycle tracking.

Inputs

days

Results

Estimated Ovulation

January 15

Fertile Window StartJanuary 10
Fertile Window EndJanuary 16
Next PeriodJanuary 29

Estimated Ovulation

January 15

How to Use This Calculator
  1. Start by filling in the input fields below. Results update instantly as you type, so you can experiment with different values to see how they affect the outcome.
  2. Cycle Length — Average menstrual cycle length. Accepts values from 20 days to 45 days (default: 28 days).
  3. Last Period Day — Day of the month your last period started. Accepts values from 1 to 31 (default: 1).
  4. Last Period Month — Month your last period started. Accepts values from 1 to 12 (default: 1).
  5. Once all inputs are set, review your results in the Results panel. Here's what each output means:
  6. Estimated Ovulation — your calculated result. This is the primary result of this calculator.
  7. Fertile Window Start — your calculated result.
  8. Fertile Window End — your calculated result.
  9. Next Period — your calculated result.
  10. Explore the related calculators below if you need deeper analysis or want to approach this topic from a different angle.
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