Share your insights or perspective on the financial matter presented in the input.

Which set of earnings is used to work out the P/E of a stock
There are two common types of P/E ratio calculations: "trailing" and "forward" (and then there are various mixes of the two). Trailing P/E ratios are calculated as [current price] / [trailing 12-month EPS]. An alternative is the Forward P/E ratio, which is based on an estimate of earnings in the coming 12 months. The estimate used is usually called "consensus" and, to answer your question, is the average estimate of analysts who cover the stock. Any reputable organization will disclose how they calculate their financials. For example, Reuters uses a trailing ratio (indicated by "TTM") on their page for BHP. So, the first reason a PE ratio might not jump on an announcement is it might be forward looking and therefore not very sensitive to the realized earnings. The second reason is that if it is a trailing ratio, some of the annual EPS change is known prior to the annual announcement. For example, on 12/31 a company might report a large drop in annual earnings, but if the bulk of that loss was reported in a previous quarterly report, then the trailing EPS would account partially for it prior to the annual announcement.  In this case, I think the first reason is the culprit. The Reuters P/E of nearly 12 is a trailing ratio, so if you see 8 I'd think it must be based on a forward-looking estimate.