Sharpe ratio vs profit factor: how to judge a trading system

The two numbers people reach for are the profit factor and the Sharpe ratio. One measures the size of the edge, the other how bumpy the ride is. Neither is the whole picture, and each misleads in its own way for a once-a-day futures system. Here is what each says, where each lies, and why the number you should plan around is a third one entirely.

Profit factor, in one line

Sharpe ratio, in one line

The Sharpe ratio is the average return above the risk-free rate, divided by the standard deviation of those returns. In plain terms: return per unit of volatility. A high Sharpe means the returns arrived smoothly; a low one means the same profit arrived on a rougher road. It was designed to compare investments on a risk-adjusted basis rather than on raw return alone, so a strategy that makes 20% with wild swings can score worse than one that makes 12% calmly.

That is a useful idea, because the system with the same total profit are not equally easy to own; the one with the lower Sharpe is the one you are more likely to abandon at the worst moment. But the ratio was built for a world of continuous, roughly bell-shaped returns, and a stop-and-target futures system is not that world.

What each one hides

The row worth staring at is the third one. Both metrics are silent on the depth of the worst stretch, and that is the number you actually have to sit through.

Why Sharpe misleads for a once-a-day system

The Sharpe ratio assumes returns are roughly normal, a smooth bell curve of small ups and downs. A system that takes one trade a day with a fixed stop and a target at three times the risk does not produce that shape. It produces a lumpy, two-humped distribution: mostly a full winner or a full loser, with little in between. Feeding that into a formula built for a bell curve gives a number that is defined but conceptually strained.

Three more problems stack on top. First, Sharpe penalizes upside volatility exactly as much as downside: a system with occasional large winners is marked down for the very outcomes you want, which is why the Sortino ratio, using only downside deviation, is often fairer. Second, it is interval-sensitive: compute it on daily returns and you get one number, on monthly returns another. Third, over a short window it is noisy, so a Sharpe from a few months of data is close to meaningless. None of this makes Sharpe useless; it makes a single quoted Sharpe number one to treat with suspicion unless you know how it was computed.

A Sharpe ratio with no measurement interval attached is like a speed with no unit. It is a number that sounds precise and means nothing until you ask how it was taken.

The number that beats both: drawdown

That is the figure to plan around, because it is the one you live through. A great profit factor and a great Sharpe are cold comfort at the bottom of a drawdown you did not expect and cannot stomach. Before you weigh any ratio, decide whether you would have kept going through that low point, because most people who fail with a working system fail exactly there. The full treatment is in what drawdown is, and the arithmetic of what it all nets out to is in how much a trading bot actually makes.

How to use them together

If a vendor leads with a single dramatic ratio and will not show you the trade list, the drawdown, or the sample size behind it, that is the tell. One number in isolation is a marketing decision, not a measurement. Which metrics a serious system exposes, and why, is part of the guide to trading systems.

Frequently asked questions

What is a good Sharpe ratio for trading?

There is no universal threshold, and quoting one without saying how it was measured is close to meaningless, because the same strategy produces different Sharpe numbers on daily, monthly and per-trade returns. Broadly, a Sharpe above 1 is often called good and above 2 excellent for a diversified portfolio, but those benchmarks were set for continuous, roughly normal returns, not a lumpy once-a-day stop-and-target system. Treat any single Sharpe figure with suspicion unless you know the measurement interval and sample length behind it.

Which is better, Sharpe ratio or profit factor?

Neither, because they answer different questions. Profit factor tells you how large the edge is; the Sharpe ratio tells you how smoothly the returns arrived. A system can score well on one and ordinarily on the other, so relying on a single metric hides exactly the trait the other would reveal. The practical answer is to read both, then plan your account around the maximum drawdown, the number that actually determines whether you stay in the seat.

Why does a once-a-day system break the Sharpe ratio?

Because the Sharpe ratio assumes returns follow a smooth bell curve, and a system that takes one trade a day with a fixed stop and target produces a lumpy, two-humped distribution instead: mostly full winners or full losers. It also penalizes big winning trades as if they were risk, and its value changes with whether you measure daily or monthly. The Sortino ratio, which counts only downside volatility, is usually fairer for this kind of strategy.

Educational content, not investment advice. Trading futures involves substantial risk of loss and is not suitable for every investor. Any reference to Algomyth results is hypothetical, simulated over historical data, and shown in full on the performance page; past performance does not guarantee future results.