Average Fill Price | Spot Trading & Execution

SPOT TRADING & EXECUTION · EXECUTION MECHANICS

Average fill price is the quantity-weighted average of all executions generated by an order. It converts multiple fills at different prices into one economically meaningful execution price.

Risk first. A simple arithmetic mean of fill prices is wrong when fill sizes differ. Average fill price also usually excludes trading fees, so it should not be confused with total all-in acquisition or disposal cost.

Last reviewed: 21 August 2026 · Educational content only

Concept
Calculation
Benchmarks
Worked example
Mistakes
Checkpoint
FAQ
Summary

Weight each execution by quantity

Average fill price = Σ(fill price × fill quantity) ÷ Σ(fill quantity)

If one execution represents 90% of the order and another only 10%, the larger execution must dominate the average. This is the same volume-weighting logic commonly described as order-level VWAP.

The metric is especially useful for marketable orders that walk the book and for passive orders that fill gradually across several timestamps.

Separate price from fees and other costs

Measure	Includes	Does not necessarily include
Average fill price	Executed prices weighted by quantity	Trading fees, network fees, financing
Gross trade value	Fill price × quantity	Fee impact unless explicitly added
Net cash cost/proceeds	Trade value adjusted for trading fees	External transfer/network costs unless added
Implementation shortfall	Difference versus chosen benchmark plus execution effects	Requires a defined benchmark and consistent methodology

Fee currency matters: some venues deduct fees in quote currency, base asset or a separate exchange token. Reconcile the actual account movement rather than assuming fees simply add to price.

Average fill is not an execution-quality verdict

Arrival price

Compare average fill with the market reference when the decision/order began.

Mid-price

Useful neutral reference, but not directly executable for size.

Limit price

Shows whether fills stayed inside the allowed boundary; does not measure missed opportunity.

Post-trade markout

Shows how market price moved after execution, useful for diagnosing adverse selection.

A good average fill can still be poor relative to the opportunity set if the order waited too long; a worse-looking average can be reasonable if the market moved sharply during execution.

Worked example

A buy order receives three fills: 0.2 BTC at £80,000, 0.5 BTC at £80,100 and 0.3 BTC at £80,300.

Weighted cost = (0.2×80,000) + (0.5×80,100) + (0.3×80,300) = £16,000 + £40,050 + £24,090 = £80,140 Average fill = £80,140 ÷ 1.0 BTC = £80,140

The simple mean of the three prices would be £80,133.33, which is wrong because the fill sizes differ.

If the venue then charges a 0.10% taker fee in quote currency, the fee is £80.14, so the all-in cash outlay becomes £80,220.14 even though the average fill price remains £80,140.

From average fill to implementation shortfall

Average fill answers “where did the executed quantity trade?” A fuller execution review asks “how did that compare with the market when the decision was made?” Suppose the arrival mid-price for the 1 BTC example was £80,050 and the average fill was £80,140. The gross price shortfall for the buy is £90 per BTC before fees.

Price shortfall = average buy fill − benchmark = £80,140 − £80,050 = £90

Add the £80.14 fee from the example and the immediate all-in shortfall versus that benchmark becomes £170.14. This still does not capture opportunity cost on any quantity that never filled, so execution analysis should state whether it measures only executed quantity or the full intended order.

Benchmark discipline: use a benchmark chosen before reviewing the outcome. Selecting whichever reference makes a fill look best after the fact undermines the comparison.

Common mistakes and misunderstandings

Taking the simple mean of fill prices without weighting by size.
Including unfilled quantity in the average.
Calling average fill price the same thing as all-in cost after fees.
Comparing two orders using different benchmarks or timestamps.
Ignoring fee currency and actual account debits/credits.

Execution discipline: Reconcile three layers separately: executed quantity and average fill, trading fees, then benchmark-relative execution quality.

Knowledge checkpoint

Q1. Why is the simple mean of £80,000 and £81,000 wrong if 90% of the quantity filled at the first price?

Q2. Does average fill normally include taker/maker fees?

Q3. Which quantity belongs in the denominator: requested quantity or executed quantity?

Q4. Why can two identical average fills represent different execution quality if the market path was different?

Self-check: A strong answer should explain both the order instruction and the execution consequence, including what can happen if liquidity or venue state changes.

FAQ

❓ Is average fill price the same as VWAP?

At order level it is a quantity-weighted average of that order’s fills, which is VWAP logic. It is not necessarily the same as market-wide VWAP over a time window.

❓ Do unfilled quantities affect average fill?

No. Only executed fills belong in the calculation.

❓ Are fees included?

Usually the displayed average fill is based on execution prices before fees; calculate all-in cash cost separately.

❓ Can a single order have one average fill but many trade IDs?

Yes. Multiple executions can be aggregated into one order-level average.

Summary

Average fill price weights each execution price by the quantity filled there.
Only executed quantity belongs in the calculation.
Trading fees and other costs should be reconciled separately.
Benchmark comparison is needed to judge execution quality rather than merely calculate price.

This building block explains execution mechanics and risk. It is not a recommendation, signal or instruction to trade any cryptoasset.