When Did I Conceive Calculator: First Response
Use this calculator to estimate your conception date based on the date you received a positive result on a First Response pregnancy test. First Response Early Result tests are known for their high sensitivity, often detecting pregnancy several days before a missed period.
Understanding Your First Response Positive and Conception
A positive result on a First Response Early Result (FRER) pregnancy test is an exciting moment! These tests are designed to detect very low levels of the pregnancy hormone, human chorionic gonadotropin (hCG), in your urine. This sensitivity allows them to often detect pregnancy up to six days before your missed period.
How First Response Tests Work
First Response tests work by detecting hCG, a hormone produced by the placenta shortly after a fertilized egg implants in the uterine wall. Implantation typically occurs 6 to 12 days after ovulation (DPO), with an average of 9 DPO. Once implantation occurs, hCG levels begin to rise rapidly, roughly doubling every 48 to 72 hours.
The high sensitivity of First Response tests means they can pick up hCG levels as low as 6.3 mIU/mL. This allows for earlier detection compared to many other home pregnancy tests. While some women may get a positive as early as 8 DPO, it's more common to see a clear positive around 9-10 DPO, or later if implantation occurred on the later side of the 6-12 DPO window.
Estimating Your Conception Date
Because implantation and the subsequent rise in hCG can vary, and because a positive test can occur at different points in the early stages of pregnancy, estimating your exact conception date based solely on a positive test provides a range rather than a single day. Our calculator uses the following logic:
- We assume that a positive First Response test typically indicates you are between 8 and 12 days past ovulation (DPO).
- By subtracting this range of days from your positive test date, we can estimate your conception window.
- For example, if you tested positive on a First Response test, the earliest you might have conceived would be approximately 12 days before your test date (assuming a later implantation/detection), and the latest you might have conceived would be approximately 8 days before your test date (assuming an earlier implantation/detection).
Factors Affecting the Estimate
Several factors can influence the accuracy of this estimate:
- Individual hCG Levels: The rate at which hCG rises varies from person to person.
- Implantation Day: Implantation can happen anywhere from 6 to 12 DPO.
- Test Sensitivity: While FRERs are highly sensitive, the exact threshold for your specific test might vary slightly.
- Urine Concentration: Your urine concentration can affect how early hCG is detectable.
This calculator provides a helpful estimate, but for a more precise due date and to confirm your pregnancy, always consult with your healthcare provider. They can perform blood tests to measure hCG levels and conduct ultrasounds to determine gestational age more accurately.