Honestly, the best thing you could do is ask him if there's anything you can do/how he wants you to handle his stuttering. I could (and will) spout off advice, but in reality every person who stutters is comfortable handling interactions differently, and my experience probably won’t be exactly the same as his. I think it’s super important for people to be open about stuttering, and you bringing it up will probably generate a good discussion with him, and will make communication much easier (for both of you) than if you were to just follow the suggestions of somebody on the internet. 1. Don't assume that it's okay to try to finish his sentences. I WOULD just say "don't finish his sentences" but in some situations I'm actually okay with people doing this. Only certain people, like my mom and my boyfriend. People I'm very close to. Since he's your father, maybe you're close enough that he'd be okay with this. 2. Maintain eye contact. Don't pretend it's not happening. I knew people who would rummage around and do other things as if I'd stopped talking. They'd ignore it because they were probably uncomfortable, but it was rude. Just make it clear that you're still listening, you're still engaged, and you still want to know what he's saying. 3. Understand that stuttering isn't related to anxiety or nerves. Personally my stuttering is more prevalent when I first wake up, or when I'm tired or grumpy, or if I haven't said much all day. But it's also kind of unpredictable, and really it's a part of my speech all the time. I guess what I'm saying is don't take it personally if he stutters more around you for any reason. I probably have a lot more to say on the subject... Let me know if you have any questions!