Adding % sign to value in textbox

In my win-form, I am binding a textbox to a property, populated through my object. The property returns a number. Let's say 55.5
I want to add a % sign at the end of this 55.5 without changing the decimal or any of the significant figures.
How can i do it?

Here is what i know so far:
In the binding panel in the text property, under the "Format type" menu, there is a "Custom" option. It has Custom format textbox. If we put the % sign in here in a correct way, it will just be added to the end of the value of the property. So far, 0.0% or 0.00% has not worked as it changes the decimal and significant figures.

Any insight will be appreciated.