When Did I Conceive?

When Did I Conceive—and Can I Know Who the Father Is?

So, you’re pregnant—and now you’re wondering: When did I conceive? And maybe even, Can I figure out who the father is? These are common and valid questions.

Need answers now? Text anonymously with a nurse for free at (208) 944-1004.

While pinpointing the exact moment of conception isn't an exact science, your body’s natural cycle can offer helpful clues.

What Date Did I Conceive?

Whether you’re just a few weeks along or already into your second trimester, you can estimate your conception date with some basic information about your cycle.

Most people ovulate—meaning they release an egg that can be fertilized—about two weeks after the first day of their last period. This ovulation window usually lasts two to three days, and it’s during this time that pregnancy most commonly occurs.

Conception Date Calculator

If you know the first day of your last menstrual period (LMP), you can estimate your ovulation window and, in turn, when you likely conceived.

Here’s the basic formula: LMP + ~14 days = estimated ovulation

Keep in mind that this is just an estimate. If your cycle is shorter or longer than average (which is around 28 days), your ovulation day may be earlier or later.

There are also helpful online tools that can do the math for you, or you can simply text us at (208) 944-1004 for help figuring it out.

Also worth noting: sperm can live inside the female reproductive system for up to five days.¹ ² That means intercourse a few days before ovulation can still result in pregnancy. So even if your timing seems off, conception might have still occurred.

Conception Calculator

First Day of Your Last Period:

Average Length of Cycles:

Conception Date from Ultrasound

Ultrasound is one of the most reliable ways to estimate when you conceived. During early pregnancy, fetal development follows a fairly consistent timeline. Measuring the size of the embryo or fetus can help determine how far along you are and give you a more precise conception window.

An ultrasound can also confirm that the pregnancy is progressing normally and rule out complications like miscarriage or ectopic pregnancy.³

While most OBGYN clinics offer ultrasounds, they often involve insurance, appointments, and paperwork. Lifeline Pregnancy Resource Center provides free limited ultrasounds—no insurance required.

Get Help Determining Your Conception Date

If you're unsure about when you got pregnant or have questions about what this means for you, you don’t have to navigate it alone.

Reach out to a licensed nurse by texting (208) 944-1004 for free, anonymous answers. Whether you’re trying to estimate your conception date, explore your pregnancy options, or just talk to someone who understands, we’re here for you.

Sources:

1. https://www.mayoclinic.org/healthy-lifestyle/getting-pregnant/expert-answers/ovulation-signs/faq-20058000

2. https://my.clevelandclinic.org/health/articles/23439-ovulation

3. https://my.clevelandclinic.org/health/diagnostics/9704-ultrasound-in-pregnancy