Pregnancy Conception Calculator
Estimate your due date, conception date, and fertile window instantly.
Due Date
Last Period
Ultrasound
Results will appear here.
Our free Pregnancy Conception Calculator helps you estimate your conception date, due date, and fertile window using three methods — your due date, last menstrual period, or ultrasound results. Simply pick the method that matches what you already know and get your results instantly.
How to Use This Calculator
1
Choose your calculation method — Due Date, Last Period, or Ultrasound — using the tabs at the top.
2
If using Last Period, enter the first day of your last menstrual period and select your average cycle length.
3
If using Ultrasound, enter the scan date and the gestational age your doctor provided in weeks and days.
4
Click Calculate to instantly see your estimated conception date, due date, and current gestational age.
5
Review your possible conception window — a 6-day range showing when fertilization most likely occurred.
Which Calculation Method Should You Use?
| Method | Best When | Cycle Needed | Accuracy |
|---|---|---|---|
| Due Date | Doctor has already given you an EDD | No | Good |
| Last Menstrual Period | You know your last period date and have regular cycles | Yes | Moderate |
| Ultrasound | You have early scan results with gestational age | No | Most Accurate |
Frequently Asked Questions
Not with complete certainty. Sperm can survive inside the body for up to 5 days, which means fertilization may have happened a few days after intercourse. This calculator gives you a well-informed estimate and a conception window — not a single exact date. For the most accurate dating, an early ultrasound between 6 and 10 weeks is your best option.
If your cycles are irregular, the Last Period method will be less reliable since it assumes a predictable ovulation schedule. In that case, use the Ultrasound tab instead — it calculates conception date based on actual fetal measurements, which are much more accurate regardless of your cycle pattern.
The conception window is a 6-day range during which pregnancy could have occurred — 5 days before your estimated ovulation date through the day of ovulation itself. This accounts for how long sperm can survive in the reproductive tract. The calculator displays this window automatically alongside your conception date estimate.
The gestational age shown is calculated from your estimated last menstrual period to today's date. It is a reliable estimate when your LMP is known accurately. Keep in mind that gestational age counts from your last period — not from the actual conception date — which is why it appears about 2 weeks longer than the time since conception.
Want to Understand Conception Dating in Depth?
Read our complete guide — LMP method, due date method, ultrasound dating, and tips for irregular cycles all explained simply.