# Execution Cost > The total cost of converting a trading decision into a position — spread, commissions and fees, slippage, market impact, financing, and the opportunity cost of orders that were rejected or never filled. - Canonical: https://hadalinstruments.com/glossary/execution-cost/ - Term set: https://hadalinstruments.com/glossary/ --- Execution cost is everything the market charges between the decision and the position. The framework that takes it seriously is implementation shortfall, proposed by Perold in 1988: compare the paper portfolio, which transacts instantly at decision prices in unlimited size, against the real one. The difference is the true cost of execution, and it is always larger than the visible line items. The components differ sharply in visibility. **Spread** is the most visible and the most advertised — though advertised spreads are averages drawn from calm regimes, not from the moments a trader's orders actually cluster in. **Commissions and financing** appear on statements. **[Slippage](/glossary/slippage/)** appears only if decision prices were recorded. **Market impact** — the price moving because the order itself consumed liquidity — is invisible without careful measurement. Least visible of all is the cost of orders that never became trades: fills refused under [last look](/glossary/last-look/), [requotes](/glossary/requote/) declined, entries missed while the price ran. A cost accounting that omits the unfilled orders is a survivor-only accounting. The backtest implication is direct. Most simulations model execution cost as a single flat number — a fixed spread, a fixed slippage allowance — when the real quantity is regime-dependent and correlated with exactly the events a strategy trades. A stop triggered during [spread widening](/glossary/spread-widening/) does not pay the average; it pays the event regime. Flattering the cost assumption is one of the quietest ways a dead strategy stays alive on paper. The honest property of execution cost is that it is measurable from records the trader already owns: order timestamps, quoted prices, fill prices, and statements are sufficient to reconstruct the distribution — not the anecdote — of what execution actually cost. The [Execution Cost Auditor](/instruments/execution-cost-auditor/) I am building is intended to compute exactly that from imported statements, because retail transaction-cost analysis effectively does not exist. ## Commonly confused with Neighbouring concepts that get used interchangeably, and the distinction that actually separates them. - **[Implementation shortfall](https://hadalinstruments.com/glossary/implementation-shortfall/)** — Shortfall is the measurement framework; execution cost is the quantity it measures. Perold's construction compares a paper portfolio transacting instantly at decision prices against the real one, and the gap is the cost. Treating them as synonyms hides the fact that you can accept the framework and still measure it badly. - **[Slippage](https://hadalinstruments.com/glossary/slippage/)** — One component of the total, alongside spread, fees, impact, financing and unfilled orders. Reporting slippage as though it were execution cost is the most common way a broker comparison ends up measuring the wrong thing. - **[Spread](https://hadalinstruments.com/glossary/spread-widening/)** — The most visible component, and therefore the one most often mistaken for the whole. Spread is also the component most reliably advertised, which means a venue can compete on the visible line while the invisible ones move in the other direction. - **[Market impact](https://hadalinstruments.com/glossary/market-impact/)** — Impact is the price moving because your own order consumed liquidity. It is a component of execution cost and it is invisible without deliberate measurement, which is why cost accountings assembled from statements alone systematically omit it. ## How to measure it in your own data A definition you cannot test is a definition you have to take on trust. This is the shortest honest route from the concept to a number you computed yourself. - **Records you need** — Order timestamps, the price quoted when the decision was made, fill prices, and account statements for commissions and financing. Critically, also the attempts that never became trades — rejections and declined requotes. Fills and statements are ordinarily in an account holder's records; the decision price and the rejected attempts are the two that platforms most often discard, and finding out which of them yours keeps comes before any of the arithmetic. - **What you compute** — Reconstruct the paper portfolio that transacts instantly at decision prices, then subtract what actually happened. Report the distribution rather than the average: a single mean figure hides that cost is regime-dependent and correlated with the events the strategy trades. - **What the answer tells you** — A cost accounting that omits the unfilled orders is a survivor-only accounting, and it flatters every venue that declines fills rather than pricing them badly. If your measured cost is flat across regimes, that is usually evidence about your measurement rather than about your execution. ## Questions and answers ### Is execution cost just the spread plus commission? No, and the components that are missing from that sum are the ones you cannot see on a statement. Slippage requires recorded decision prices. Market impact requires deliberate measurement. Financing appears late. And the cost of orders that never filled at all — refused under last look, requoted and declined, missed while the price ran — appears nowhere unless you go looking. ### What is implementation shortfall? The framework, proposed by Perold in 1988, for measuring what execution actually costs: compare a paper portfolio that transacts instantly at decision prices in unlimited size against the real portfolio that had to work its way into the market. The difference is the true cost, and it is always larger than the visible line items. ### Why is my live execution cost worse than my backtest assumed? Because most simulations model it as a single flat number — a fixed spread and a fixed slippage allowance — while the real quantity varies with regime and is correlated with the events the strategy trades on. A stop triggered during a widening event does not pay the average; it pays the regime it fired in. ### Can I measure execution cost myself? Yes, and this is the useful part: the inputs are records you already own. Order timestamps, quoted prices at decision, fill prices and statements are sufficient to reconstruct the distribution of what execution actually cost you — not the anecdote of the one trade that went badly, which is what most traders are working from. ## If this has already cost you What execution has actually cost you, decomposed rather than averaged, comes out of records your broker already sends you. - [Execution-Cost Assay](https://hadalinstruments.com/assays/#execution-cost-assay) “What is my execution actually costing me?” Will not establish: Whether your broker is acting against you. Cost is measurable from your side; intent is not, and a report that claimed otherwise would be selling you a story. Intake is not open yet, so none of these can be commissioned today. They are listed here so you know the measurement exists and what it would and would not settle — the [launch list](https://hadalinstruments.com/pricing/#waitlist) hears first. ## Work it out yourself Free calculators that take this concept as an input. Each shows its working, so the number it gives you can be checked rather than taken on trust. - [Forex profit calculator](https://hadalinstruments.com/tools/forex-profit-calculator/) Net result, costs included · Gross — the other calculators’ figure - [Pip value calculator](https://hadalinstruments.com/tools/pip-value-calculator/) One pip per lot, and at your size · The conventions, stated and editable - [Risk reward calculator](https://hadalinstruments.com/tools/risk-reward-calculator/) R:R, chart distances and net of costs · Break-even win rate under each ## Related terms Derived from the links this entry makes and the entries that link back to it. - [Anchored VWAP](https://hadalinstruments.com/glossary/anchored-vwap/) The volume-weighted average price computed from a chosen starting event forward — the session VWAP's generalisation, where the anchor is an election and the line is only as meaningful as the anchor's case. - [Implementation Shortfall](https://hadalinstruments.com/glossary/implementation-shortfall/) The difference between the return of a paper portfolio traded instantly at the decision price and the return actually realised, including the cost of the quantity that never filled at all. - [Information Coefficient (IC)](https://hadalinstruments.com/glossary/information-coefficient/) The correlation between a forecast and the outcome it predicted — the standard scalar summary of how accurate a signal was, measured across a cross-section or through time. - [Last Look](https://hadalinstruments.com/glossary/last-look/) A practice in over-the-counter foreign exchange in which a liquidity provider, after receiving an order against its quoted price, retains a final window in which to accept or reject the trade. - [Market Impact](https://hadalinstruments.com/glossary/market-impact/) The adverse price movement caused by an order's own execution — the difference between the prices that existed before the order began and the prices it had to reach in order to complete. - [Requote](https://hadalinstruments.com/glossary/requote/) A venue's response to an order that offers a new price instead of a fill, obliging the trader to accept the revised price, retry, or abandon the trade. - [Slippage](https://hadalinstruments.com/glossary/slippage/) The difference between the price at which a trade was expected to execute and the price at which it actually filled, signed so that positive slippage favours the trader and negative slippage costs them. - [Spread Widening](https://hadalinstruments.com/glossary/spread-widening/) A transient expansion of the bid-ask spread beyond its typical range, most commonly around scheduled news releases, liquidity transitions, and session rollovers. ## Where the term is used Instrument pages whose published copy uses this term. Each page states what it measures and what it does not establish. - [Execution Cost Auditor](https://hadalinstruments.com/instruments/execution-cost-auditor/) Statement-import truth about what your execution actually cost. Feed & Execution ## In the research Execution Cost comes up in seven research notes on this site, and this entry lists three of them. - [Why did my broker charge me so much in swaps?](https://hadalinstruments.com/research/why-did-my-broker-charge-me-so-much-in-swaps/) Because a swap is two costs wearing one name: an interest-rate differential anyone can compute, and a residual on top of it that almost nobody checks. - [Why is my live spread wider than my backtest?](https://hadalinstruments.com/research/why-is-my-live-spread-wider-than-my-backtest/) Usually because the backtest used a spread that never existed. Here is how to find which of the four causes is yours, and what each one costs you. - [The edge that was real and worth half a pip](https://hadalinstruments.com/research/the-edge-that-was-real-and-worth-half-a-pip/) My engine's first end-to-end edge hunt found statistically real structure — leans of half to two percent from a coin flip — and none of it is tradable. ## Cite This Definition APA BibTeX HTML Hadal Instruments. (2026). Execution Cost. Hadal Glossary. https://hadalinstruments.com/glossary/execution-cost/ Version 426b66a, 2026-08-25. @misc{hadal_2026_execution-cost, author = {Hadal Instruments}, title = {Execution Cost}, year = {2026}, url = {https://hadalinstruments.com/glossary/execution-cost/}, howpublished = {Hadal Glossary}, version = {426b66a}, note = {Pre-launch publication; version dated 2026-08-25} } Source: Hadal Instruments, Execution Cost. Original Research Copy Citation **Version 426b66a** identifies the commit that last changed this page in Hadal's content repository. That repository is not public, so the identifier does not resolve externally — it is published so a citation pins one specific state rather than a moving page. To obtain the exact version cited, use the [press and research route](https://hadalinstruments.com/press/).