Forward P/E

The Price-to-Earnings ratio calculated using analysts' forecast of next-twelve-months (NTM) earnings instead of the past twelve months (TTM). It tells you how expensive a stock is relative to where earnings are expected to be, not where they've been.

Why it matters: Trailing P/E looks backward, which is misleading for growing or recovering companies. A stock with collapsing earnings has a deceptively low trailing P/E. A high-growth company with rapidly rising earnings has a deceptively high trailing P/E. Forward P/E adjusts for both.

The catch: Forward P/E is only as good as the analyst estimates behind it. Wall Street analysts are notoriously optimistic - on average, consensus earnings forecasts at the start of the year overshoot actual reported earnings by about 7%. During recessions, the miss is much wider. So a "cheap" forward P/E might just be a stale estimate that hasn't been cut yet.

Pros use both: trailing P/E for what you can prove, forward P/E for what the market is paying for. The difference between them shows whether the market expects earnings to grow or shrink.