Trailing or forward earnings to calculate SP500?

What is the trailing PE of the S&P 500?

Price to earnings ratio, based on trailing twelve month “as reported” earnings. Current PE is estimated from latest reported earnings and current market price. Source: Robert Shiller and his book Irrational Exuberance for historic S&P 500 PE Ratio.
S&P 500 PE Ratio.

Mean:	15.97
Median:	14.89
Min:	5.31	(Dec 1917)
Max:	123.73	(May 2009)

What is Tesla’s PE ratio?

95.46

The PE ratio is a simple way to assess whether a stock is over or under valued and is the most widely used valuation measure. Tesla PE ratio as of June 03, 2022 is 95.46.