"Earnings" is a plural noun. Some nouns, like "earnings", only have a plural form and cannot be used in the singular.
"Earnings" is a plural noun. Some nouns, like "earnings", only have a plural form and cannot be used in the singular. They are known as pluralia tantum (Latin for "plural only").
She declared her earnings to the tax authorities.
She declared her earning to the tax authorities.
Follow the same strategy with the expressions average earnings, net earnings, gross earnings, quarterly earnings, annual earnings, hourly/weekly/monthly earnings, etc.
The company will announce its quarterly earnings on April 12.
The term "earning" (without "s") is an adjective, not a noun.
The earning ability of a chemical engineer is really high.
The earning of a chemical engineer is really high.
Note that pluralia tantum take a pronoun and a verb in the plural. For example, you can say "earnings are/have", not "earnings is/has".
The company’s earnings have fallen over the last four years.
The company’s earnings has fallen over the last four years.
A partial list of other plural nouns related to money or financial assets:
