--- title: "Permanent Price Impact: Formula, Meaning" description: "Permanent price impact is the part of a trade's price effect that persists after short-lived liquidity effects fade, measured as the signed change in the..." canonical: https://www.getswoopr.com/indicators/market-microstructure/permanent-price-impact/ source: "Swoopr Investment: https://www.getswoopr.com" --- ## Direct Answer > Permanent price impact is the part of a trade's price effect that persists after short-lived liquidity effects fade, measured as the signed change in the midpoint from before the trade to a later time. It is usually read as the information content of the trade. A positive value means price stayed in the direction of the trade, which suggests the trade carried information. # Permanent Price Impact: Formula, Meaning, Signals, Examples and How to Use It ## How Is Permanent Price Impact Calculated? Permanent price impact is the part of a trade's price effect that persists after short-lived liquidity effects fade, measured as the signed change in the midpoint from before the trade to a later time. It is usually read as the information content of the trade. **Formula:** `Permanent Impact = D x (Midpoint at t+delta - Midpoint at t) / Midpoint at t, with delta long enough for temporary effects to fade` **Inputs:** - Midpoint at trade time - Midpoint at a later time t+delta - Trade direction D **Worked example.** A buyer-initiated trade with the midpoint rising from 50.00 to 50.04 has a permanent price impact of 0.08%. The inputs are illustrative numbers, not market data. **Reading it.** A positive value means price stayed in the direction of the trade, which suggests the trade carried information. It plus the realized spread makes up the effective spread (using the twofold convention in both). **Limits.** The horizon delta is a choice, and later midpoint changes include news and unrelated flow, so some of the 'permanent' effect is not caused by the trade. The convention for factors of two differs across papers. ## What is Permanent Price Impact? Permanent price impact is the part of a trade's price effect that persists after short-lived liquidity effects fade, measured as the signed change in the midpoint from before the trade to a later time. It is usually read as the information content of the trade. ## How to use Permanent Price Impact A positive value means price stayed in the direction of the trade, which suggests the trade carried information. It plus the realized spread makes up the effective spread (using the twofold convention in both). A reading alone is never a buy or sell signal; it needs context from price structure, volume, volatility and the broader market regime. ## Strengths - Waiting for a later midpoint lets short-lived liquidity effects fade, so it isolates the part of the move that remains. - Signed by trade direction and scaled by the pre-trade midpoint, impacts from buys and sells average on one scale. - Reproducible when the formula and data convention are fixed. ## Weaknesses and limitations - A longer horizon lets more information unrelated to the trade arrive, so noise in the estimate rises with delta. - For a single trade the measure is mostly noise, so it becomes meaningful only when averaged over many trades by size bucket. - Correlated indicators can create false confidence by repeating the same underlying information. ## Editorial and risk note This page is educational content, not individualized investment advice. It should not imply guaranteed prediction, accuracy or outperformance. ## Frequently Asked Questions Is Permanent Price Impact a buy or sell signal? No. A positive value means price stayed in the direction of the trade, which suggests the trade carried information. The horizon delta is a choice, and later midpoint changes include news and unrelated flow, so some of the 'permanent' effect is not caused by the trade. A trade built on it still needs a trigger, an invalidation rule, a position size and realistic execution assumptions. What is the best setting for Permanent Price Impact? Permanent Price Impact is computed from midpoint at trade time; midpoint at a later time t+delta; trade direction D, so the choices that matter are the data convention and the window it is read over. Test those across instruments, regimes and out-of-sample periods instead of fitting one historical winner. Can Permanent Price Impact be used by itself? The horizon delta is a choice, and later midpoint changes include news and unrelated flow, so some of the 'permanent' effect is not caused by the trade. The convention for factors of two differs across papers. For that reason it is read next to measures of direction, participation, valuation, liquidity and risk, not alone. Does Permanent Price Impact work on every timeframe? The calculation (Permanent Impact = D x (Midpoint at t+delta - Midpoint at t) / Midpoint at t, with delta long enough for temporary effects to fade) can be run on any bar size, but behavior is not portable: a reading on a five-minute chart describes a very different market window from the same reading on a daily chart. Validate the exact timeframe before relying on it. Why does Permanent Price Impact give false signals? A longer horizon lets more information unrelated to the trade arrive, so noise in the estimate rises with delta. For a single trade the measure is mostly noise, so it becomes meaningful only when averaged over many trades by size bucket. Lag, noise and regime changes add to this, because market participants react to new information after the reading is calculated. How should Permanent Price Impact be backtested? Rebuild Permanent Price Impact from midpoint at trade time using point-in-time data, write the rules before testing, include delisted securities where relevant, model realistic fills and costs, reserve a validation sample and compare with a simpler baseline. ## References - [Econometrica: Continuous Auctions and Insider Trading (Kyle, 1985)](https://doi.org/10.2307/1913210) S Swoopr Editorial Team The Swoopr Editorial Team produces independent investment education, research, and tools for understanding markets, evaluating opportunities, and managing risk. All content is educational only and does not constitute personalized investment advice. See our [editorial policy](https://www.getswoopr.com/legal/editorial-policy/) and [corrections policy](https://www.getswoopr.com/legal/corrections-policy/).