I have a minimum value and a maximum value (The values can change).
I also have a value that is in between of these two values.
private int minValue = 201;
private int maxValue = 500;
private int currentValue = 482
I think what you want to have is this calculation:
double percentage = (currentValue - minValue) / (maxValue - minValue);
Just like @kevin-esche wrote in the comments.