Quarter (Q1, Q2, Q3, Q4)

A three-month period on a financial calendar that acts as a basis for the reporting of earnings and the paying of dividends.

Investopedia Says:
Quarters are important because all public companies must report their results on a quarterly basis.

You'll hear the following abbreviations:
Q1 - January, February, and March
Q2 - April, May, and June
Q3 - July, August, and September
Q4 - October, November, December

For example, if earnings per share were $1.50 in Q1, this means earnings were $1.50 for the period of January, February and March.

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