Trying to pinpoint your due date from a specific event? Whether you know the date of intercourse or your estimated conception date, our calculator accounts for key biological factors to give you the most accurate possible timeline.
Birth Probability Calendar
Pregnancy Progress
Current Status
Key Dates
A Note on Accuracy: Why Intercourse Date ≠ Conception Date
Many online calculators make the mistake of treating the date of intercourse and the date of conception as the same thing. This is not biologically correct. Sperm can live for up to 5 days inside the body, meaning conception (fertilization) can happen several days after intercourse.
Our tool is more accurate because it correctly models this delay by adding an average 2-day period between intercourse and conception, providing a more realistic due date estimate.
How to Use This Calculator & Read Your Results
Our tool is designed to be simple to use and provide a rich, detailed timeline. Here’s how to get your results in just a few steps.
- Choose Your Method: Select whether you know your Intercourse Date (the default) or your Conception Date using the toggle at the top.
- Enter Your Date: Click the input field and use the calendar to select the specific date you have in mind.
- Calculate Your Timeline: Click the “Calculate Due Date >” button.
- Explore Your Results: Your full, personalized timeline will appear, including your estimated due date, pregnancy progress, and the interactive Birth Probability Calendar.
Understanding Your Birth Probability Calendar
Only about 4% of babies are born on their exact due date. Our interactive calendar gives you a much more realistic picture by showing the statistical likelihood of birth for each day surrounding your due date.
- The Colors: The calendar uses a color gradient to show the Likely Birth Window. Lighter pink shades indicate a lower but increasing chance, while the vibrant, darker pinks highlight the days with the peak probability of going into labor.
- The Percentages: Each day in the window shows a percentage. This is the statistical probability of giving birth on that specific day based on large-scale population data.
- The Due Date: The green square marks your Est. Due Date. This is the single day with the highest statistical probability and the center of your “peak week.”
The Science: From a Single Day to a Full Timeline
Calculating a due date from a specific event requires a more nuanced approach than just simple addition. Our calculator uses a clinical model based on key biological milestones.
- If you enter a Conception Date: This is the most direct method. We simply add 266 days (38 weeks)—the standard length of a pregnancy from conception to birth—to find your estimated due date.¹
- If you enter an Intercourse Date: This is where our calculator stands out. We first account for the fact that sperm can survive for up to 5 days and fertilization doesn’t happen instantly. We estimate your conception date to be approximately 2 days after intercourse. From that more realistic conception date, we then add 266 days to calculate your final due date.
Frequently Asked Questions
Which input method is more accurate?
Entering a known “Conception Date” (for example, from an IVF procedure) will be the most precise. However, entering your “Intercourse Date” is a very strong estimate, and our calculator’s model is designed to give you the most likely outcome.
What if I had sex on multiple days?
For the most accurate estimate, enter the earliest date of intercourse that occurred within your fertile window. Our calculator’s model, which accounts for sperm survival, will provide the best timeline based on that information.
Why shouldn’t I just add 280 days to my intercourse date?
This is a common mistake. The 280-day (40-week) pregnancy length is measured from your Last Menstrual Period (LMP), not from intercourse or conception. Calculating from conception requires using the fetal age of 266 days (38 weeks), which our tool does automatically.
What if I don’t know my intercourse or conception date?
No problem! Our main Due Date Calculator allows you to calculate your due date from your Last Menstrual Period (LMP), which is the most common and reliable method for most people.
This information is for educational purposes and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult with a healthcare provider for any health concerns or to confirm your pregnancy timeline.
References
¹ The American College of Obstetricians and Gynecologists (ACOG). (2017). Methods for Estimating the Due Date. Committee Opinion No. 700.