Deductions & credits

I know my sons father is self employed but it is not his business and it is not consistent. He will not sure his income with me, I’m pretty sure i made more but because he does not share this with me am i suppose to take the risk of just claiming to see who gets it or what do you suggest i do? My custody agreement form does state 182.50 each although like you said one of us probably had him for more over nights than the other.