Earnings per share is the number that travels. It leads the headline and anchors the comparison with last year. It is also the final step in a chain of calculations, and each link in that chain can move it for a different reason.
Airbnb's quarterly report for the three months ended Sept. 30, filed with the Securities and Exchange Commission on Nov. 5, is a useful worked example. Its diluted earnings per share rose to $3.16 from $2.21 a year earlier, a gain of about 43 percent. Revenue rose about 19 percent. Per-share profit grew more than twice as fast as sales because of three things: wider operating profit, a smaller tax bill and fewer shares.