The thing is you will find yourself in the same spot over and over again so you will learn quite quickly whether you are getting the correct odds or not at a glance.
For instance with only two players in the pot, any bet above half the pot size is giving you incorrect odds (unless you are on a straight flush draw with KQ over pairs).
You don't need to be able to figure out the exact odds because usually it's a simple yes or no. Most players use standard bets when playing online e.g. half pot / three quarters / pot / all-in because they have set up buttons to do this.
I am sticking to the Rule Of 2 here, the rule of 4 only applies if you are calling an all-in bet or you know you will not be raised after the turn.