Right now it's used as a study and there's another full sized bathroom and bedroom in the basement. So I was thinking just a powder room would suffice. But will this affect resale?

yes it will i'm afraid.

but that doesnt mean that you shouldnt add a powder room on this floor. then at least dinner guests wouldnt have to use your private bathroom.

and you could certainly add a door to the 2 bedrooms/bathroom 'suite' which would give you the same privacy but not break your house.

Do you plan on your guests to use your Master Bathroom as the bathroom when visiting or do you expect them to go downstairs? Honestly, that doesn't sound like a good idea for resale, no. I would recommend adding on to get the extra space for a Bathroom if that is possible. - Stephanei

You could move the closet in the master bedroom next to the door like the layout in the other bedroom. You could then make the front 1/3 of the bath into a powder room and the back 2/3 into your master. might have to switch to a shower and use pocket doors to save on space.

I like Wendy's idea thanks!