See your estimated pregnancy odds for each day in a typical cycle. Enter the start date of your last period and your average cycle length to see a research-based calendar of approximate chances.
Phase:
Calendar values are statistical estimates based on research averages and the information you enter. They cannot confirm pregnancy, rule out pregnancy, or replace advice from your own clinician.
How to Use the Pregnancy Chance Calendar
Enter Your Cycle Details:
- Select your typical menstrual cycle length (e.g., 28 days) and input the start date of your most recent period.
- For advanced personalised estimates, enter additional details such as age, height, weight, average weekly work hours, daily cigarette use, and weekly alcohol intake. These inputs help the calculator estimate your likely ovulation day, fertile window, and a personalised range of daily pregnancy chances in the model.
- Press Calculate to generate your personalized calendar.
Interpret the Calendar:
- Dark Red Cell: Indicates the first day of your period.
- Light Red Cells: Show estimated menstruation days.
- Light Blue Cells: Highlight your fertile window (days when pregnancy is most likely).
- Dark Blue Cell: Marks your highest-chance day for pregnancy.
- Green Cell: Indicates your estimated ovulation day.
- Cells outside these periods show minimal pregnancy chances (<0.1%).
- Percentages and colours are model-based estimates from research averages. They are not a diagnosis or a guarantee for any single cycle.
Pregnancy Chances:
- Each calendar date displays a percentage (e.g., “12%”) at the bottom.
- This percentage represents the model's estimated likelihood of pregnancy if intercourse occurs on that day, based on your inputs (including contraceptives entered) and published fertility research. It cannot confirm pregnancy or predict exactly what will happen for you.
How It Works
This calendar estimates ovulation from the period date and average cycle length you enter. Faust et al. (2019) and Wilcox et al. (1995) describe how conception chances change around estimated ovulation in study populations. They support the broad pattern used here, not the exact percentage shown for an individual cycle.
- Fertile Window: Days the calendar estimates as more likely for conception.
- Approximate Ovulation: The estimated day when an egg may be released.
- Highest Chance Day: Usually the day before estimated ovulation, based on the pattern reported by Faust et al.
- Next Period: Based on the average cycle length you enter.
- Pregnancy Test Day: Approximately 14 days after estimated ovulation. The FDA says urine hCG may be detectable 12 to 15 days after ovulation in a 28-day cycle, but an early negative result can be wrong.
- Estimated Due Date: Based on the standard 280-day LMP method, adjusted for cycle length. ACOG explains that LMP dating assumes a 28-day cycle and ovulation on day 14.
- Estimated Pregnancy Chance Per Day: A simplified estimate, not a measured personal probability.
The calendar below your results updates as you change your information or move between months.
Evidence and Limits
Faust and Wilcox inform the broad day-by-day pattern around ovulation. The percentages shown also use simplified adjustments for age, lifestyle and other details you enter. The exact percentages and combined adjustments were not measured or validated as one personal prediction in those studies.
If you select contraception, the starting figures come from first-year typical- and perfect-use estimates reported by Trussell (2011). A first-year failure rate is not a published one-day rate, so its use in this calendar remains an approximation.
Calendar estimates cannot confirm ovulation. Cycle timing can vary from month to month.
Health Disclaimer
This calculator provides an approximation of your menstrual phases and fertility window based on average biological patterns. It relies on the accuracy of the period-start date and cycle length you enter - note that no one knows the length of their current menstrual cycle until the cycle has completed. All results are estimates and may change. This tool is intended for informational purposes only and is not medical advice. Always consult a healthcare professional for personalized guidance on fertility, pregnancy, and reproductive health.