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Trailing P/E vs Forward P/E: Which Number to Trust
Trailing P/E uses the last twelve months of reported earnings; forward P/E uses analyst estimates for the next twelve. Trailing is grounded; forward is optimistic (analyst consensus has overshot S&P 500 EPS by 6.9% per year on average since 1998 per FactSet). Check both on any stock quote page before drawing a conclusion.
Trailing P/E vs Forward P/E at a Glance
The two ratios share a numerator (price) and split on the denominator: which earnings to use. Both are variants of the P/E ratio.
| Dimension | Trailing P/E | Forward P/E |
|---|---|---|
| Earnings used | Reported, last twelve months | Analyst estimate, next twelve months |
| Reliability | Audited, fixed | Forecast, revised quarterly |
| Where it lies | Distorted by one-offs and cycle peaks | Carries persistent analyst optimism |
| S&P 500 long-run avg | About 19.6 (Yardeni, post-1936) | About 18.6 over the last 10 years (FactSet) |
| Goes to N/A when | Earnings are negative | Coverage is thin or guidance is pulled |
| Best for | Mature, stable-EPS businesses | Recovery stories and loss-making growth |
Trailing always lags. Forward always carries forecast risk. Both can look cheap or rich depending on which one you read at the same moment.
What Trailing P/E Tells You
Trailing P/E divides today's price by the last twelve months of reported earnings per share. The number is anchored in audited filings, which is its main appeal: nothing about it depends on a forecast. Yardeni's long-run series puts the post-1936 S&P 500 average around 19.6. Sectors stretch that wide: utilities and banks have historically run in the 12-15 range, software well above 25.
Trailing P/E breaks in two predictable places. Cyclicals look cheapest at the peak. An automaker on a 6x trailing P/E at the top of the cycle is reporting peak earnings that are about to fall. Six months later the price has dropped and the trailing ratio jumps because EPS has fallen faster than price. The 2008-2009 episode is the textbook case: aggregate S&P 500 quarterly EPS turned briefly negative in Q4 2008, and trailing P/E spiked above 120x in Q1 2009, exactly at the bottom.
The other failure mode is one-off items. A divestiture gain or a tax benefit inflates the last twelve months of earnings per share and depresses trailing P/E for a quarter or two. Read the footnotes; check whether the trailing number sits on GAAP or non-GAAP earnings before comparing peers.
What Forward P/E Tells You
Forward P/E divides today's price by an analyst-consensus estimate of the next twelve months of earnings per share. Wall Street, FactSet, Yardeni, and most sell-side notes default to this version. The reason is forward-looking: a stock's price reflects what investors expect to happen, so dividing by what is expected to be earned matches the question better than dividing by what was earned.
The catch is that the estimate itself is biased. FactSet's 25-year study (1998-2022) found that start-of-year analyst estimates of S&P 500 EPS turned out to be 6.9% too high on average, with overestimates in 17 of 25 years. McKinsey put the same point more bluntly: across 25 years analysts forecast 10-12% annual EPS growth against actual 6%. Backtests by Wesley Gray and others show that sorting stocks cheap-to-expensive on forward earnings yield has underperformed the same sort on trailing earnings yield in the US, UK, eurozone, and Japan.
Forward P/E also breaks at cyclical peaks. The denominator is built by analysts extrapolating recent strength, so peak-cycle forward P/E looks deceptively low for the same reason trailing P/E does: the E is too high. The COVID episode showed the opposite distortion. The S&P 500 forward 12-month P/E reached 23.4 on 2 September 2020 because price recovered faster than analysts cut their forecasts.
When to Use Each
Trailing P/E and forward P/E reward different situations. Pick the one the company actually fits.
| Situation | Trailing P/E | Forward P/E | Why |
|---|---|---|---|
| Mature, stable earnings | Strong | Marginal | Past EPS is a fair proxy for next year |
| High-growth or recovery story | Misleading | Strong | Trailing reflects last year's smaller business |
| Loss-making firm | Undefined | Required | Negative EPS breaks trailing entirely |
| Cyclical at the peak | Misleading (peak earnings) | Misleading (peak forecasts) | Both lean on numbers about to mean-revert |
| Crisis bottom | Misleading (crashed EPS) | Strong | Trailing spikes after EPS collapse |
Use trailing P/E for mature, slow-changing businesses where last year is a credible guide to next year, and as a sanity check against forward P/E that has drifted from reality.
Use forward P/E when the next twelve months will not look like the last (recovery, post-crisis, fast growth) and accept the optimism bias as the cost of getting a forward signal at all.
Avoid both at cyclical extremes. Pair the multiple with a cyclical stocks read and lean on normalized earnings instead.
Using Both Together
The gap between the two ratios is more useful than either one alone.
A forward P/E far below trailing says analysts expect EPS to climb sharply over the next twelve months. A forward P/E above trailing means analysts expect EPS to fall. The direction tells you what consensus is pricing in; the size tells you how much. When the gap matches your own view of the business, the consensus is reasonable. When it diverges, you have either an edge or a blind spot.
Pair the two with one capital-structure-neutral metric. EV/EBITDA ignores capital structure and tax jurisdiction, so it stays useful when leverage is unusual or peers report under different tax regimes. Net income, and the resulting P/E, can flatter a debt-heavy firm that EV/EBITDA reveals as expensive.
Damodaran's textbook rule still applies. If you are valuing a company on trailing EPS, the multiple you compare against must also be trailing. Mixing trailing EPS with a forward-P/E benchmark double-counts growth; the same holds in reverse.
For the next layer of decomposition, growth-adjusted multiples like P/E vs PEG split the question further: how much of the gap is growth, how much is mispricing.
Open any stock quote page to see trailing and forward P/E side by side, with the EV/EBITDA, margin, and EPS context that puts them in perspective.
Frequently Asked Questions
Why is trailing P/E undefined for unprofitable companies? Trailing P/E divides price by the last twelve months of earnings per share. When EPS is negative, the ratio either flips sign or gets reported as N/A by data providers, since "you pay 30x negative earnings" has no useful interpretation. This is why analysts default to forward P/E for loss-making growth companies, where trailing simply does not work.
Does trailing P/E or forward P/E predict returns better? Backtests by Wesley Gray and replications cited by the CFA Institute show that sorting stocks cheap-to-expensive on trailing earnings yield has historically outperformed the same sort on forward earnings yield in the US, UK, eurozone, and Japan. The reason is the optimism bias in analyst forecasts: forward earnings yield looks most attractive on stocks where consensus is too high, which is the wrong moment to buy.
What does NTM P/E mean and how is it different from forward P/E? NTM stands for next-twelve-months. NTM P/E uses a rolling 12-month consensus EPS, blended from the current and next fiscal-year estimates depending on where in the year you are. Some sources use "forward P/E" to mean FY1, the current fiscal year only, which becomes a shorter horizon as the year progresses. FactSet's "12-month forward" series is NTM; Morningstar's "forward P/E" is FY1. They are not interchangeable.
How does the S&P 500 forward P/E compare to its long-run average? FactSet reported a forward 12-month P/E of 23.1 on 29 October 2025, against a 5-year average of 19.9 and a 10-year average of 18.6. The headline forward number alone overstates how much earnings power has improved: a 2.0% average overestimate in analyst forecasts excluding crisis years means today's denominator is structurally too high.