How to calculate CR2032 battery life with LED
You can only rely on the (Amp Hour) the battery has. Or for small batteries the mAh (milli amp hour). Anyway all these figures are estimates anyway. The lifetimes depends e.g. on temperature. 

I don't know what you need the LED for but you can get LEDs which are a lot more efficient: 1 mA would give you 20x as long. 

As K H said: you are wasting energy in a series resistor: Try to find a switching current source. A simple PWM circuit with an inductor comes to mind.