Might help of you backed up 4 ft so we could see the entire side clear down to the base.

 

Fair point lol it's attached! It's a small bathroom so about the best I could do

 

Use a level to check if the wall and or the cupboard is plumb.
Maybe the floor is not level?
Plumb vs level. Easily confused with each other. #constructiontips #tr... | TikTok

 

Looks like the countertop is in contact with the wall but back of the vanity is not flush to the countertop.

Can move the countertop ?

 

Second picture … top looks flush with the side of the cabinet. We need a bigger picture. And a level. Cabinet or wall could be off.

 

If you caulk it then the vanity can't move without stretching the caulk. And the caulking will look good for like 1 month and then get dusty and dirty.

If you can't live with the gap then add some baseboard and a 1/4 round shoe right there to create an artificial lip.

 

New picture seems to show base in the way.

 

Bad picture on my part, we cut out the baseboard to fit and it is definitely against the wall next to the baseboard. Unless I am missing something?

 

So if you have a gap on the back left side all the way from the bottom to the top, it could be because the wall is bowed or the corner is not square and the back of the cabinet is hitting the wall before the side does. Or maybe you left some nails sticking out when you removed the baseboard. Or it could just be caught on the floor. Try lifting it up in the air before you push it back down.

 

Will do! Will try this. Any ideas for how to fill the gap if that does not work?

 

A scribe strip of molding to cover the gap.

 

A 1.5-inch quarter round, and it is gone.

ED

 

See if shimming the front of the vanity helps.

I just had to do it for a fancy utility sink combo. It was the best solution within budget and under the circumstances.

 

Then you just transfer the gap from the side to the base.

And still need quarter round to conceal it.

ED

 

If there are side gaps after everything seems to fit tight at the base and the vanity is level and plumb in the front, the best recourse is to add a short backsplash plus two side splashes to cover the possible framing/sheetrock variations. Then, if there is still gap at the top of the straight splash, caulk and paint.

 

First you find the problem and then solve it.
Was the cupboard built out of square?
Is the floor level?
Is the wall plumb?