Maximum days that you can still get BFP

So let’s say you track everything, ovulate and BD in your window and don’t BD again in the TWW. I know you can start getting BFP 9/10dpo but what about the maximum DPO that pregnancy still possible. If you are a few days into your missed period and the last time you BD was ovulation window. When would you get a BFP if you ovulated later and implantation occur the latest possible. Is it 14 days past the last time you BD?? You’re not out until AF shows but if you have irregular periods do you just have to keep testing until a positive or AF?? Seems like there would be a maximum anoint of time that you’d be possibly pregnant and not need to bother testing.