add on
phrasal verb.to include something extra to what you already have or are buying.
phrasal verb.to include or attach an additional element to an existing entity or total; often used in commercial or construction contexts.
“They add on a service charge at the end of the meal.”
“When you book your flight online, the airline often tries to add on extra insurance or seat selection fees.”
“The developers plan to add on a new wing to the hospital to accommodate the growing number of patients in the district.”
commonly used with costs, fees, or physical extensions to buildings.
distinguish from the noun 'add-on' (hyphenated) which refers to the extra item itself; as a verb, it is often used in the passive voice regarding taxes or fees.
when 'add on' is followed by a destination or target, the preposition 'to' is required after the particle 'on'.