For greetings for the New Year, say:

• “Ketiva V'Chatima Tova”

              From: Rosh Chodesh Elul
              Until:  Eve of (erev) Rosh Hashana (when the holiday begins).

• “L'Shana Tova Tikateiv V'Tichateim”

            From:  First night of Rosh Hashana (when the holiday begins)
            Until:   Musaf of the first day of Rosh Hashana.

• “Gmar Chatima Tova”

               From:  Musaf Rosh Hashana
               Until:   End of Yom Kippur.

• “Gmar Tov”

               From: Yom Kippur
               Until:  Musaf Hoshana Rabba.