using a tip120 darlington transistor

is there any calculators out there that will be able to tell me the Ic current of the transistor given the base current and Vc. Well the base current will be the same current drawn from one digital output of the arduino board and im going to hook up 12v to the collector pin. I need to know Ic becuase i am trying to drive a bunch of leds and i need to know if im giving too much current or not enough? Any help will be appreciated, thanks

Well the base current will be the same current drawn from one digital output of the arduino board

No don't do it. If you don't have a current limiting resistor in the base then you will pull too much current out of the arduino pin and damage the output.