Long vs Short Strategies

How long and short positions work, why they behave differently, and what to consider when backtesting each direction.

Long vs Short Strategies

Every trade in a backtest has a direction. A long position profits when the price goes up. A short position profits when the price goes down. The direction you choose determines how every part of the trade works -- how profit and loss are calculated, how spreads are applied, and how stop-losses and take-profits behave.

This article explains how long and short positions work, how they differ mechanically, and what to consider when backtesting each direction.

What Is a Long Position?

Going long means buying an asset with the expectation that its price will rise. You buy at a lower price and sell at a higher price. The difference is your profit.

If you buy at 100 and the price moves to 110, you made 10%. If the price drops to 90, you lost 10%. The math is straightforward: profit equals the exit price minus the entry price, divided by the entry price.

What Is a Short Position?

Going short means selling an asset you do not own, with the expectation that its price will fall. You sell at a higher price and buy it back (cover) at a lower price. The difference is your profit.

If you short at 100 and the price drops to 90, you made 10%. If the price rises to 110, you lost 10%. The math is inverted: profit equals the entry price minus the exit price, divided by the entry price.

How can you sell something you don't own?

In real trading, your broker lends you the asset so you can sell it immediately. Later, you buy it back on the market and return it. In a backtest, the mechanics are simpler -- the engine just tracks that you entered a short position at a certain price and calculates profit or loss when you exit. The concept is the same: you profit when the price falls between your entry and exit.

Key Differences

Profit and Loss

Long and short positions have opposite P&L profiles. A long position makes money when the price rises and loses money when it falls. A short position makes money when the price falls and loses money when it rises.

There is also an asymmetry in potential outcomes. A long position can lose at most 100% of the invested amount (if the price goes to zero), but the potential gain is unlimited -- the price can keep rising. A short position is the reverse: the maximum gain is 100% (if the price goes to zero), but the potential loss is unlimited -- the price can keep rising with no ceiling.

Short losses are theoretically unlimited

When you are long, the worst case is the asset going to zero. When you are short, there is no ceiling on how far the price can rise against you. With leverage, this risk is amplified further. A short position at high leverage on a rapidly rising asset can wipe out an account quickly.

Spread Application

The spread is applied in opposite directions for long and short positions, reflecting how real markets work.

For a long trade: you buy at the ask and sell at the bid. For a short trade: you sell at the bid and buy back at the ask.

The total spread cost is the same in both directions -- you pay the full spread on every round trip.

Stop-Loss and Take-Profit Levels

Stop-loss and take-profit levels are always set as a percentage distance from the entry price, but the direction flips for short positions.

For a long trade with a 5% stop-loss: the stop is placed 5% below the entry price. If you entered at 100, the stop triggers at 95. The take-profit is placed above -- a 10% take-profit triggers at 110.

For a short trade with a 5% stop-loss: the stop is placed 5% above the entry price. If you entered at 100, the stop triggers at 105 (price rising against you is the danger direction). The take-profit is below -- a 10% take-profit triggers at 90 (price falling is the profit direction).

Benchmark Comparison

When you run a long strategy, the natural benchmark is buy-and-hold -- just holding the asset. If the asset went up 20% and your long strategy returned 25%, you beat the benchmark by 5%.

For a short strategy, the comparison is less intuitive. A short strategy profits when the asset falls, so comparing it against buy-and-hold during a bull market will always look unfavorable. Short strategies are designed for different conditions, and alpha and beta become more useful than raw return comparison when evaluating them.

Choosing a Direction

In Simula, each backtest runs in a single direction -- either long or short. You select the direction before running the backtest, and all trades in that run follow that direction. To compare both directions, run two separate backtests with the same conditions and compare the results.

Your entry and exit conditions stay the same regardless of direction. The engine interprets them relative to the position type. For example, a "crossed over" entry condition opens a long position when running long and opens a short position when running short. This lets you test whether the same signal works in both directions without rebuilding the strategy.

Same signal, different direction

Running the same strategy as both long and short is a useful diagnostic. If a moving average crossover generates strong returns as a long strategy but loses money as a short strategy, that tells you the signal is capturing upward momentum specifically -- not a symmetric pattern. If it works in both directions, the underlying signal may be more robust.

Considerations for Short Strategies

Markets Have an Upward Bias

Over long time periods, most equity markets trend upward. This means short strategies are fighting the prevailing direction of the market. A short strategy needs a clear edge to overcome this headwind. On shorter timeframes, this bias is less pronounced -- intraday price movements go both ways regardless of the long-term trend.

Forex and Crypto Are More Symmetric

Currency pairs and crypto pairs do not have the same structural upward bias as stocks. EUR/USD going up means EUR is strengthening against USD -- neither direction is inherently more likely over time. This makes forex and crypto more natural candidates for short strategies than equities.

Cost Sensitivity

In live trading, short positions can carry additional costs (borrowing fees, funding rates) that do not apply to longs. Simula's backtest does not model these additional costs, so short strategy results may be slightly more optimistic than live performance. Setting a slightly wider spread or commission can help compensate for this.

Where to Go Next

Entry & Exit Conditions -- the signals that trigger trades in either direction.

Stop-Loss, Take-Profit & Trailing Stops -- protective exits that work differently for long and short.

Spreads, Commissions & Slippage -- how trading costs apply in both directions.

Leverage & Position Sizing -- how leverage amplifies both long and short outcomes.

Benchmarks & Relative Performance -- comparing strategy results against buy-and-hold.