In a Taxi 2

深夜早朝２割増、２２時から５時まで
しんやそうちょう２わりまし、２２じから５じまで
Late at night and early in the morning there is a 20% surcharge, from 10pm to 5am.

I would call it a 'surcharge' but you might say 'premium'. 割　（わり）　is also a signifier for a 'unit of ten percent', so I think the surcharge would be 20%. It wouldn't make sense for it to only be 2%.