Expected Value | Timeless Market Theory

Expected value (EV) is the average outcome of a decision repeated many times. It is the bedrock idea beneath all serious trading and gambling: not "will this trade work?" but "if I took this exact bet a thousand times, would I come out ahead?" Master it and every other decision — what to trade, how big to bet, where to stop, when to exit — becomes a single question: is this positive EV, and where is it highest?

EV weighs how often you win against how much you win versus lose. Positive after costs = a trade worth taking.

The four variables

Probability of winning, average win, probability of losing, average loss. That's it. The result tells you, on average, how much you make or lose per trade. Positive after fees = take it; zero or negative = skip it.

Win rate is a trap

You don't need to be right often — you need to be right big. A trader can win 25% of the time and thrive if winners dwarf losers; another can win 90% and thrive by cutting losses tiny. Both work if EV is positive.

Think in probabilities, not outcomes

You can lose on a good (positive-EV) trade and win on a terrible one. The single outcome means nothing; the quality of the decision, repeated, is everything. (See process over outcome.)

Measure in R

Define risk as 1 "R" (the distance to your stop). Then express every outcome in R-multiples — a winner might be +1.7R, a loser −1R. This normalizes EV across trades of different dollar sizes.

You estimate EV; you never truly know it

Risk is easy to measure (your stop). Win rate and average reward are harder — you approximate them through backtesting, forward testing a demo account, and experience. Your long-run P&L curve is itself a verdict on whether your trades are +EV.

EV is dynamic

Like a poker hand, EV changes as a trade unfolds — the flop, the next print, fresh news. So you add when EV improves, reduce when it worsens, and get flat when it goes negative. Trading is the art of perceiving EV moment to moment and sizing to it.

Where this comes from — and how the pros say it

EV isn't a trading invention — it's basic probability, and it's the heart of every edge-based game from blackjack to insurance. In trading it's often called expectancy; Van Tharp built much of Trade Your Way to Financial Freedom around expectancy and position sizing, and it underpins how casinos, market makers, and quant funds all operate. Modern prop trader Lance Breitstein calls it "by far the most important concept in all of trading," and frames every decision — sizing, stops, when to add — as a question of expected value.

WATCH Lance Breitstein — "The First Step in Every Winning Trade (How to Find Expected Value)"