Chance = ( Final - Start) ( 1 -		1	)
		e t / τ

Where,

Final = Value of calculated variable after infinite time(its ultimate value)
Start = Initial value of calculated variable
e = Euler’s number ( 2.7182818)
t = Time in seconds
τ = Time constant for circuit in seconds

Calculating time at specified voltage or current

t = τ ( ln		1	)
	1 -	Change
		Final - Start