Forward P/E vs trailing P/E

Trailing and forward P/E share the same numerator, the current share price, but divide it by different earnings. Trailing P/E looks back at profit the company has already reported. Forward P/E looks ahead at profit that analysts expect. Knowing which one you are reading, and how it was built, is the first step toward using either sensibly.

Definitions

Trailing P/E = price / EPS over the last four reported quarters (TTM)
Forward P/E  = price / expected EPS for the next 12 months or next fiscal year

"Forward" has no single standard definition. Some sources use the next fiscal year, some blend the next four quarters, and the estimate is usually a consensus (an average of analyst forecasts). Estimates can also be on a GAAP basis or on an adjusted basis that excludes certain items. When two websites show different forward P/Es for the same stock, this is usually why.

The trailing figure is easier to pin down because it comes from reported results in SEC filings. Even so, it matters whether the EPS is basic or diluted; see basic vs diluted EPS.

Example (illustrative numbers)

A stock trades at $100. Over the last four quarters it earned $4.00 per share. Analysts expect $5.00 over the next year.

The forward ratio is lower because earnings are expected to rise. The gap itself carries information. Dividing one ratio by the other gives the growth the estimates imply:

Implied EPS growth = trailing P/E / forward P/E - 1
                   = 25 / 20 - 1 = 25%

Now flip the case. If analysts expected only $3.20 for the coming year, the forward P/E would be $100 / $3.20 = 31.25, higher than the trailing 25. A forward P/E above the trailing P/E signals that earnings are expected to fall, or that the trailing figure was flattered by something unusual.

Strengths and weaknesses of each

Trailing P/E

• Built on results the company has actually reported, so it is verifiable.
• Backward-looking. After a recession, an acquisition or a large one-time charge, last year's profit may say little about next year's.

Forward P/E

• Closer to what a buyer cares about, which is future earnings.
• Depends entirely on forecasts, and forecasts are opinions. Research has repeatedly found that analyst estimates tend to lean optimistic, particularly for periods further out. A forward P/E that looks reasonable on optimistic estimates may be less reasonable than it appears.

Neither is "right". They answer different questions, and looking at both together is more informative than choosing one.

When the two diverge a lot

• Forward well below trailing. Either earnings are expected to grow strongly, or the trailing number was depressed by a one-off cost. Check which.
• Forward above trailing. Earnings are expected to decline, or the trailing figure included an unusual gain.
• Cyclical companies. Near a profit peak, trailing P/E looks low while the forward figure may already reflect the downturn. Near a trough, the reverse happens: trailing looks very high and forward looks lower. Compare with normalized earnings before drawing conclusions.
• Acquisitions and spin-offs. Reported history may not match the business that exists today.

Rules of thumb

• Check how "forward" is defined before comparing. Next fiscal year and next twelve months are not the same, particularly for a company mid-year.
• Do not compare one company's trailing P/E with another's forward P/E, or a GAAP ratio with an adjusted one.
• Look at the gap, not just the level. A big gap means the forward ratio depends heavily on a forecast coming true.
• Remember that estimates get revised. A forward P/E is a snapshot of expectations on a given day. For more on how expectations are formed, see analyst ratings and price targets.
• Pair either ratio with growth. The PEG ratio does this in a simple, imperfect way.

Common mistakes

• Treating the forward P/E as a prediction. It is today's price divided by someone's estimate, not a promise about earnings.
• Ignoring that low forward P/E on a shrinking business may be a trap rather than a bargain.
• Comparing across sectors. Both measures vary a lot by industry; see the basics in the P/E ratio.

Where to see it on StocksXray

StocksXray builds its valuation on reported figures from SEC filings and end-of-day prices, and it presents fair value as a range rather than a single forecast. The methodology page describes the approach.

Key takeaways

• Trailing P/E divides price by the last four quarters of reported EPS; forward P/E divides it by expected EPS.
• The ratio of the two implies the growth embedded in the estimates.
• Forward P/E depends on forecasts, which tend to run optimistic, and has no single definition.
• Compare like with like: same basis, same period, same sector.