What formula is used to calculate earnings per share for an etf like SPY? What do they use for the numerator(earnings)?
Is it the earnings of the underlying companies weighted by their percentage in the index SPX?
You're right, it's the aggregated earnings of the company shares owned by the ETF.
The numerator is done like this: For each company the fund owns, multiply EPS for that company times the number of shares the fund owns. Add those together and that's aggregate earnings.
Divide that by number of shares outstanding, and that's earnings per share.