Perhaps the best way to remember is that milliAmp isn't the basic unit - Amp is. It's the same way when calculating low pass frequency - don't use microFs, use Fs. and so on... For most electronics equations, you use the basic unit.
Another thing is you'll soon learn to estimate what values you'd expect from a calculation, e.g. if the resistor value worked out to be 1mhm: or 100k then you'd be reasonably sure it's wrong.