How do I say dates in German?
Use ordinal numbers. The day is always dative when preceded by am (on).
Heute ist der erste Mai. (Today is May 1st.)
Am dritten Juli. (On July 3rd.)
Am fünfundzwanzigsten Dezember. (On December 25th.)
Example
Mein Geburtstag ist am zwölften August. (My birthday is on August 12th.)