The growth cycle will slow gradually on the surface when the roots run out of room. If you think that it's close hold the plant at the base and gradually wiggle the pot off the plant. You will know right then if it is "root-bound". Little dirt will fall and the plant will hold the shape of the pot. The roots will be everywhere causing it to hold it's shape. Roots are pretty tough so do not be scared. When you move to a bigger pot do this. Put a mound of soil in the middle of the pot about half way full. Grab hold of the plant in the exact bottom of the root system and separate a good bit of the roots. They need to be broken out of that mold, (the smaller pot) so they can grow out again. Cover the rest of the roots and pack the soil pretty good so the plant will remain upright during the first few watering. Then just sit back and watch it grow exponentially.