Pokemon Go Hub has developed a calculator that will help players understand what their chances are when they attempt to catch any given Pokemon.
The calculator is based on something called the Grand Unified Catch Theory (GUCT), which is a surprisingly complicated formula that takes into account the type of Poke Ball used, the Pokemon's species, the throw bonus and more.
Using this formula, Pokemon Go Hub put together an easy-to-use calculator that will show you how likely you are to catch a Pokemon out in the wild depending on a wide variety of variables.
In order to determine your percentage chance of catching a Pokemon, you need to choose the Pokemon from the drop-down list, enter your trainer level, choose any relevant medal bonuses and note whether you threw a curveball or used a Razzberry. Click the Calculate button and you will see your chances to catch the Pokemon (depending on whether or not you get a catch bonus).
According to Pokemon Go Hub, "this is the first Catch chance calculator that uses the correct formulas and probability." Although its utility is relatively limited, it might help you decide when to use a Razzberry or risk a curveball throw.
Go try out the Pokemon Go Catch Calculator here.