How to Use Our Conception Calculator
Our calculator gives you two methods to estimate your due date. Choose the one that best fits the information you have.
Date of Conception: This is the most accurate method if you know the exact date of ovulation. This may be the case if you were tracking ovulation with predictor kits (OPKs) or through a fertility treatment like IVF. Select this option and enter the specific date.
First Day of Last Period (LMP): This is the standard method used by doctors if the conception date is unknown. Select this option and enter the first day of your last menstrual period. The calculator will estimate your conception date occurred about 14 days after this date, which is typical for a 28-day cycle.
Understanding Your Results
Once you enter your information, the calculator provides a personalized timeline for your pregnancy. Here is a breakdown of what each result means.
1. Your Estimated Due Date: This is the predicted day you will give birth.
From Conception Date: Your due date is calculated as 266 days (or 38 weeks) from your date of conception.
From LMP: Your due date is calculated as 280 days (or 40 weeks) from the first day of your last period.
2. Fetal Age vs. Gestational Age: You will notice a two-week difference between the two calculation methods. This is the difference between “fetal age” and “gestational age,” a crucial concept in pregnancy.
Your doctor will almost always refer to your pregnancy by its gestational age. So, when they say you are “6 weeks pregnant,” your baby’s fetal age is actually 4 weeks.
3. Your Key Pregnancy Milestones: Based on your results, here is an estimated timeline of major events in your pregnancy journey.
Frequently Asked Questions
Is the conception date the same as the date I had intercourse?
Not necessarily. Conception is the moment an egg is fertilized by a sperm. Sperm can live inside the female reproductive tract for up to 5 days. This means if you had intercourse on a Monday, but you didn’t ovulate until Wednesday, your actual conception date would be Wednesday. If you know your ovulation date from tracking, use that for the most accurate result. If not, the date of intercourse is a close estimate.
How accurate is a due date calculated from conception?
It is extremely accurate—often more so than the standard LMP method—if you know the precise date of ovulation. This is why due dates for IVF pregnancies (where the exact date of fertilization is known) are so precise. If you are estimating your conception date, the result will only be as accurate as your estimate.
Why does my doctor use my Last Menstrual Period (LMP) to date my pregnancy?
Doctors use the LMP method as a standard because many women don’t know their exact date of ovulation, but most can recall the first day of their last period. It creates a universal and consistent starting point for tracking all pregnancies. Even if you know your conception date, your doctor will likely still chart your pregnancy based on the 40-week gestational age model for consistency in care and records.
What if my ultrasound gives me a different due date?
You should always trust the due date provided by an ultrasound over any calculator. An ultrasound performed in the first trimester is the gold standard for dating a pregnancy. The technician measures the baby’s “crown-rump length,” which is a very accurate indicator of fetal age. It is very common for doctors to adjust a due date based on this initial ultrasound measurement.
What are the first signs of successful conception?
Around 6 to 12 days after conception, the fertilized egg must implant into the uterine wall. During this time, some women experience implantation symptoms, which can be the earliest signs of pregnancy. These can include:
Implantation Bleeding: Light spotting (pink or brown) that is much lighter than a normal period.
Mild Cramping: Light, brief cramps in the lower abdomen.
Breast Tenderness: Hormonal changes can make breasts feel sore or heavy.
Early Fatigue: Rising progesterone levels can cause significant tiredness.
Can I use this calculator to plan for a specific due date?
Yes, you can work backward. For example, if you want to have a baby in late September 2026, you can use the calculator to see that you would need to conceive around the beginning of January 2026. This allows you to plan intercourse around your fertile window in that target month.
I don’t know my conception date or my LMP. What should I do?
If you’re unsure of both dates, that’s okay. You can make an educated guess for now to get a rough idea. However, the best course of action is to see a healthcare provider. They can order an ultrasound, which will provide the most accurate dating for your pregnancy and establish a reliable due date.
Discover More About Your Journey
As you await your first positive test, learn more about the earliest signs with our Implantation Calculator. If you are actively trying to conceive, pinpoint your most fertile days each month with our Ovulation Calculator.
