Learn Spanish (Latin America): Mi cumpleaños es el quince de enero.

In Spanish, we use regular numbers like quince for almost all days of the month. You just say el followed by the number, then de, and then the month. The only exception is the first of the month, which is el primero.

Why isn't the month enero capitalized?

In Spanish, the names of the months and the days of the week are always written with lowercase letters, unless they happen to be the very first word of a sentence.

Cumpleaños ends in an 's'. Why do we use the singular Mi and es instead of the plural Mis and son?

The word cumpleaños (birthday) is a mashup of cumple (completes) and años (years). Even though it ends in an 's', it is a singular noun when you are talking about one single birthday. That is why it uses the singular Mi (my) and es (is).

Why do we use es instead of está for a date?

When we talk about dates, times, or when an event takes place, we always use the verb ser. Es is the form of ser that we use for a single event like a birthday.