Is it possible to get pregnant the day before your period??

Hi! My husband and I had unprotected sex (condom broke ?) the day before my period started. My period came the very next day. I was just wondering if it were possible for me to be pregnant? This app says there was a 3% chance on that day but I was wondering what you all had to say about it? It was just 18 days ago so I'd say it would be too soon for a test? Any help is greatly appreciated!!