How do I tell him ?

So Based on the calculation I did I would be about 4 weeks pregnant. I’m overly stressed, confused and scared. I’m 28 yr old student and also working (where I could get maternity leave) which is good. But the BD is someone I’ve been seing on and off for the last 6 years. We have a good relation and he already has a daughter but how do I break the news? I mean my situation could have been worse but I’m still worried of what his reaction would be. Any tip on how to say it? Also what would be the next step, doctor appointements first?