Quarterly reports are issued by companies every three months. Most companies have a financial year-end of Dec. 31 and quarters that end on March 31, June 30, Sept. 30 and Dec. 31.

But some companies follow a different financial calendar and report year-ends at different times. For example, Apple Inc.'s (AAPL) financial year runs October through September. See below how the quarterly reporting cycle differs.

  Companies with financial year January- December  Apple Inc. with financial year October- September
End of Q1  March 31  December 31
End of Q2  June 30  March 31
End of Q3  September 30  June 30
End of Q4/ End of Financial Year  December 31  September 30

Quarterly reports include key accounting and financial data for a company, including gross revenue, net profit, operational expenses and cash flow. The Securities and Exchange Commission (SEC) requires issuers of publicly traded shares to file Form 10-K annually and Form 10-Q quarterly within 60 days of the end of applicable period. These forms may include more detail than quarterly and annual reports.

Quarterly reports are usually accompanied by presentations from a company's management where key performance indicator data are presented to investors and analysts. Management of firms often provide guidance for future financial results as well. These presentations are routinely followed by question and answer periods.

Analysts following companies often publish estimates of key metrics for future reporting periods. Financial publications average these estimates to arrive at street consensus estimates. Companies that exceed these estimates are said to have beaten expectations. Companies whose performances are in-line with estimates are said to have met expectations. Companies whose results are below estimates are said to have missed expectations.