Price-to-Earnings Ratio

The price-to-earnings ratio - the P/E - is a company's share price divided by its earnings per share. A $40 share with $2.00 of annual earnings per share has a P/E of 20: at the current profit, twenty years of earnings to pay back the price. The ratio is quoted as trailing (last year's earnings) or forward (the forecast), and the market's long-run average on the ASX sits in the mid-teens.

The interpretation is where the number earns its keep - and loses it. A high P/E prices fast earnings growth; a low one prices stagnation or decline. The inverse of the P/E is the earnings yield: a P/E of 20 is a 5 percent earnings yield, comparable to the yield on a term deposit, which is the comparison that makes the ratio useful against cash. The market capitalisation entry covers the price-times-shares arithmetic behind the headline, and the traps - cyclical earnings, one-off gains - are the part the ratio does not show.

The arithmetic is one division with two inputs. The share price is the market's number; the earnings per share is the company's reported profit divided by the shares on issue. A $40 price and $2.00 of EPS produce a P/E of 20; the same company doubling its earnings to $4.00 while the price sits still compresses the ratio to 10. The pe ratio calculator runs the division on any price and earnings pair, and the eps calculator covers the earnings side.

The earnings yield is the second mechanism, and the one that connects the ratio to everything else. The inverse of the P/E - earnings divided by price - is directly comparable to bond and deposit yields: a P/E of 16 is a 6.25 percent earnings yield against a term deposit at 4.5 percent. The gap is the premium the equity market offers over cash, and it is the reason valuations compress when the cash rate rises. The comparison also explains the market's mood swings: the same $2.00 of earnings supports a higher price when the alternative yield falls.

The traps are the third mechanism, and the one the ratio hides. A cyclical miner at a commodity peak reports peak earnings, which makes a 6 P/E look cheap exactly when the earnings are about to halve; the real P/E on mid-cycle earnings is double the printed one. One-off gains inflate earnings the same way - an asset sale booked as profit doubles the denominator for a single year. The forward P/E prices the forecast, and the forecast is the part that can be wrong.

For an Australian reader, the P/E is the number behind every 'the market looks expensive' conversation, and the one behind every bargain-hunting list. The ASX 200's long-run P/E sits in the mid-teens; the same index traded above 20 in optimism and below 12 in panics. MoneySmart guidance on shares treats valuation as one input alongside earnings quality and debt, and the ratio is the quickest of the three to check. The market capitalisation entry covers the size arithmetic, and the index fund entry covers the option that skips the valuation debate entirely.

A colleague named Brent (yes, that Brent) bought a miner on a 6 P/E at the top of the commodity cycle because it was 'half the market's price'. The earnings halved with the commodity price, the printed P/E doubled, and the share fell with both. Cheap against peak earnings is not cheap - it is the cycle priced once. The highest-leverage thing most Australians can do is check what the earnings were doing before trusting the ratio, and run the pe ratio calculator on mid-cycle numbers rather than the headline.