Joghurt is one of the few German words that are used in all three genders (others include Dschungel and Wimpel). In Germany, the masculine gender is by far the most common. The neuter gender is common in Austria, Switzerland, and parts of southern Germany. The feminine gender is rare and restricted to parts of Austria (including the city of Vienna).
The choice of gender determines the noun's inflection: With masculine and neuter genders, the genitive form is (des) Joghurts. With the feminine gender it is (der) Joghurt.