Worked example: stop slippage in a simple scenario
Stop slippage is what happens when an order intended to exit near a stop-loss price gets filled at a worse price than that level. The “worse” part means the account is exposed to more loss than expected. This can occur even if the stop level is defined correctly, because real execution depends on the order book, liquidity, spread, and timing.
Mechanism: stable definition vs variable conditions
A stop-loss order is typically designed to trigger when the market reaches a specified stop price, then place (or convert into) an order to execute at the best available price under the broker’s execution rules.
Stable mechanics (conceptual):
- You choose a stop price (the level that triggers the order logic).
- After triggering, the fill price is determined by available liquidity and the execution method.
- If the fill price is worse than the stop price, the difference is called stop slippage.
Variable conditions (what changes):
- Spread: If the spread widens, the “available” execution price can move away from the mid or last traded price.
- Liquidity: Thin markets can cause larger price jumps between trigger and execution.
- Speed and timing: There is often some delay between the stop triggering and the actual fill.
Because these inputs vary, outcomes are not deterministic. Any example below therefore needs explicit assumptions.
Evidence via a worked numerical example (with assumptions)
Assume:
- You trade a currency pair where profit/loss moves linearly with price.
- You place a stop-loss at 1.2000.
- The intended exit is triggered when the market reaches that stop level.
- To keep the arithmetic transparent, assume the executed price directly determines your realized price movement versus the stop.
- No commissions, swap/financing, or margin effects are included.
Scenario A (slippage occurs):
- At the moment the stop triggers, the quoted price environment changes rapidly.
- Immediately after triggering, your sell order is filled at 1.1985.
Compute the slippage amount:
- Stop price: 1.2000
- Fill price: 1.1985 (worse for a sell if you expected to exit at 1.2000)
- Price difference: 1.2000 − 1.1985 = 0.0015
If your position is sized so that a 0.0015 unfavorable move corresponds to $X loss (how $X maps depends on contract size and instrument specs), then stop slippage is the part of that loss attributable to the fill being 0.0015 worse than the stop level.
Scenario B (no slippage in this simplified sense):
- Stop price: 1.2000
- Fill price: 1.2000 (or close enough that the difference is zero for the example)
- Price difference: 0.0000
Both scenarios are compatible with the same “stop is at 1.2000” instruction. The difference comes from fill quality after triggering.
Limitations and risks (what can break the expectation)
Key material limitations and failure modes:
- Gaps or fast jumps: If the market moves through levels quickly, the next available price may be far from your stop.
- Spread widening at execution: Even if the stop level is “reached,” your sell fill may use a less favorable side of the quote.
- Latency between trigger and fill: If execution systems react after the market has moved, the fill can be worse.
- Partial fills and re-pricing: Depending on execution rules, an order may fill in parts or at varying prices, complicating the realized loss.
Independent verification typically focuses on trade confirmation details: the actual fill price, timestamps, and the order type/execution method used at trigger time.
Verification and what to ask next
To explain stop slippage accurately for a specific case, verify:
- The stop price you set.
- The actual executed fill price from the trade record.
- The order type and execution method (e.g., whether the system uses market-like behavior after trigger).
- Any relevant execution costs included in your platform’s reports.
If you want, share a generic hypothetical trade record format (stop level, side, and executed price), and you can compute the slippage difference yourself using the same assumption-driven approach above. No real-time pricing is required to do that calculation.