The word "calculates roughly" indicates an approximate estimation of a value or quantity. The antonyms for this phrase could include "calculates precisely," which reflects an accurate calculation of a value or quantity. "Calculates exactly" could also be used as the opposite phrase, signifying a perfect measurement of a particular amount. Other antonyms for "calculates roughly" might include "guesses" or "estimates," which indicate a lack of precision in determining a specific value or quantity. Alternatively, "estimates exactly" or "predicts accurately" could also be used as antonyms to imply a precise calculation or forecast.