arcgis desktop - Why is the result of a raster calculation integer when it should be decimal?

I'm trying to calculate the NDVI using raster calculator, but the result is integer instead of decimal.

NDVI = (NIR - RED)/(NIR + RED)

The result is normally in the range -1 to 1, but when i tried to calculate de result is -1, 0 and 1, and it does not have have any number in between like, -0.9 or 0.1. And i need those values so i can classify the result in term of soil occupation