Direct Answer
Fill rate is the quantity actually filled divided by the quantity ordered. It measures how much of the intended size an order or strategy managed to execute. A lower fill rate means more of the intended size was missed, which for passive limit orders reflects a trade-off with price.
Fill Rate: Formula, Meaning, Signals, Examples and How to Use It
How Is Fill Rate Calculated?
Fill rate is the quantity actually filled divided by the quantity ordered. It measures how much of the intended size an order or strategy managed to execute.
Formula: Fill Rate = filled quantity / ordered quantity
Inputs:
- Filled quantity
- Ordered quantity
- Order set (one order, a day, a strategy)
Worked example. An order for 10,000 shares that fills 8,000 has a fill rate of 80.0%. The inputs are illustrative numbers, not market data.
Reading it. A lower fill rate means more of the intended size was missed, which for passive limit orders reflects a trade-off with price. It is read together with slippage, since a high fill rate can be bought by paying more.
Limits. It is quantity-based, so it differs from fill ratio, which counts orders. It does not show how long the fill took or how far price moved on the unfilled portion, which is where implementation shortfall comes in.
What is Fill Rate?
Fill rate is the quantity actually filled divided by the quantity ordered. It measures how much of the intended size an order or strategy managed to execute.
How to use Fill Rate
A lower fill rate means more of the intended size was missed, which for passive limit orders reflects a trade-off with price. It is read together with slippage, since a high fill rate can be bought by paying more. A reading alone is never a buy or sell signal; it needs context from price structure, volume, volatility and the broader market regime.
Strengths
- Because it is quantity over quantity, it is a single bounded fraction that directly states how much of the intended size was achieved.
- It can be aggregated by weighting by order size, so a strategy-level rate reflects total shares and not the number of orders.
- Reproducible when the formula and data convention are fixed.
Weaknesses and limitations
- A passive limit-order strategy gets a lower fill rate by design, so the rate should be read alongside order type and urgency.
- Orders cancelled by the trader because price moved away count as unfilled, so fill rate mixes execution quality with changed intent.
- 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 Fill Rate a buy or sell signal?
No. A lower fill rate means more of the intended size was missed, which for passive limit orders reflects a trade-off with price. It is quantity-based, so it differs from fill ratio, which counts orders. 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 Fill Rate?
Fill Rate takes these inputs: filled quantity; ordered quantity; order set (one order, a day, a strategy). There is no universal best setting for the tunable ones, so test them across instruments, regimes and out-of-sample periods and favor stable parameter regions over one historical winner.
Can Fill Rate be used by itself?
It is quantity-based, so it differs from fill ratio, which counts orders. It does not show how long the fill took or how far price moved on the unfilled portion, which is where implementation shortfall comes in. For that reason it is read next to measures of direction, participation, valuation, liquidity and risk, not alone.
Does Fill Rate work on every timeframe?
The calculation (Fill Rate = filled quantity / ordered quantity) 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 Fill Rate give false signals?
A passive limit-order strategy gets a lower fill rate by design, so the rate should be read alongside order type and urgency. Orders cancelled by the trader because price moved away count as unfilled, so fill rate mixes execution quality with changed intent. Lag, noise and regime changes add to this, because market participants react to new information after the reading is calculated.
How should Fill Rate be backtested?
Rebuild Fill Rate from filled quantity 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.