Image zoom Credit: Getty Images. Home pregnancy tests work by detecting the presence of the hormone human chorionic gonadotropin (hCG), which shows up in your urine shortly after conception. They're available at grocery stores and pharmacies, and they're relatively easy to use. But how accurate are home pregnancy tests, and what external factors can affect the results? Here's everything you need to know. How Accurate are Pregnancy Tests? Home pregnancy tests claim to be about 99 percent accurate. Indeed, with proper use, they can detect results just as well as the urine tests you'd take at a doctor's office. Appropriate timing is crucial for getting a reliable reading.