Cat peeing outside litter box

He is a bit overweight. He has IBd issues and a heard condition. It is a jumbo box he shares with his adopted sister. I used to have two but they both only went in one. He does this at least twice or three times a week. How do I know if it's a problem or he is missing the box? He goes in the box so I'm not are. Any advice?

Where in relation to the litter box are the accidents happening?

Outside the box, some inside some over all over floor or wall

Are the accidents happening within a foot or less of the box or on opposite sides of the room? Or both? Is he peeing on a wall next to the litter box?

Yes and yes to both

Ok. Just wanted to make sure it wasnt a case where he was standing in the litter box, but peeing over the edge.

I think with his other medical issues, best to get him to the vet for a checkup. I'd consider bloodwork and a urinalysis.

He just had it done a month ago. He is in the litter box when going so not really understanding

I meant the pee was outside of te box but he's in the box

you may need a box with higher sides or even enclosed. 

WHere is this box?

Awesome! Thanks so
Much. I just bought a bigger one but didn't see the high side one.

I put my litter boxes inside a washer tray. Makes cleanup easy.http://www.homedepot.com/p/GE-30-in-x-32-in-x-2-in-Washer-Floor-Tray-PM7X1DS/202214668