Learn Spanish (Spain): Buenos días. Estoy muy bien.

In Spanish, common greetings like buenos días (good morning), buenas tardes (good afternoon), and buenas noches (good evening) are traditionally always plural. While you might hear the singular buen día in some parts of Latin America, in Spain you will almost always use the plural.

The word "días" ends in an "a". Shouldn't it be feminine and use "buenas"?

The word día (day) is one of the most famous exceptions to the Spanish rule that words ending in "a" are feminine. It is actually a masculine word (el día). Because adjectives must match the gender of the noun they describe, we use the masculine plural word buenos.

Why does this sentence use "estoy" for "I am" instead of "soy"?

Spanish has two verbs for "to be": ser and estar. We use estoy (which comes from estar) here because it describes a temporary state of being or how you are feeling at this moment. A helpful rhyme for beginners is: "How you feel and where you are, always use the verb estar."

Could I say "estoy muy bueno" instead of "estoy muy bien" to mean the same thing?

No, because bien means "well" (a word describing how you are doing), while bueno means "good" (a word describing the quality of a person or thing). Saying estoy muy bueno changes the meaning entirely and is actually used as slang in Spain to mean "I am very physically attractive." To say you are doing well, always use estoy muy bien.