Two execution prices are not enough to reconstruct an order’s average unless their quantities are known. A small fill and a much larger fill should not receive equal weight. For brokerage reporting, preserving the execution-level details makes an average reproducible and helps separate trade price from the customer’s total cost.
Follow the evidence
Trace how the event could reach markets, then inspect a competing explanation.
Compare explanations
Switch lenses to see what each account explains—and what remains uncertain.
Consider an entirely invented order filled for 30 units at 99.80 and 70 units at 100.20. The first execution contributes 2,994.00 in price-times-quantity value, and the second contributes 7,014.00. The total is 10,008.00 for 100 units, giving a quantity-weighted average of 100.08. The unweighted mean of the two displayed prices is 100.00. That figure assigns equal importance to a 30-unit execution and a 70-unit execution, so it does not reproduce the illustrated total. The correct weighting answers a specific question: the average execution price per unit for those included fills. It does not automatically answer the total-cost question. If the invented purchase also incurs a separately stated 5.00 charge, the cash outlay becomes 10,013.00 under that assumption. Dividing that amount by 100 gives 100.13 per unit including the assumed charge. A report should label those two figures separately rather than silently inserting a fee into an execution-price field.
Consider an entirely invented order filled for 30 units at 99.80 and 70 units at 100.20. The first execution contributes 2,994.00 in price-times-quantity value, and the second contributes 7,014.00. The total is 10,008.00 for 100 units, giving a quantity-weighted average of 100.08. The unweighted mean of the two displayed prices is 100.00. That figure assigns equal importance to a 30-unit execution and a 70-unit execution, so it does not reproduce the illustrated total. The correct weighting answers a specific question: the average execution price per unit for those included fills. It does not automatically answer the total-cost question. If the invented purchase also incurs a separately stated 5.00 charge, the cash outlay becomes 10,013.00 under that assumption. Dividing that amount by 100 gives 100.13 per unit including the assumed charge. A report should label those two figures separately rather than silently inserting a fee into an execution-price field.
Collect execution identifiers, quantities, prices, currency and any correction or cancellation records. Confirm that all the rows belong to the same intended order and that the total included quantity matches the quantity being summarised. Where a broker reports allocations separately, establish which allocation the average describes. Keep enough decimal precision to reproduce the total before rounding a display value. Then reconcile separately stated fees, conversion charges and settlement amounts with the appropriate records. A difference between two interfaces may reflect their calculation scope, so establish that scope before calling either value wrong. All quantities, prices and costs in the worked example are WFN assumptions. No market execution or broker-specific pricing policy is claimed. The field definition and calculation method were reviewed on 8 October 2026 to support clearer reading of execution reports.
FIX defines an order-level average field
The official FIX field documentation identifies tag 6, AvgPx, as the calculated average price of the fills on an order. It is an order-level price field, distinct from the price and quantity of an individual execution. This article uses the published FIX 4.2 field definition as its terminology reference. FIX Trading Community — FIX 4.2 AvgPx, field 6
The FIX Trading Community’s order-state documentation separately illustrates partial fills and execution corrections or cancellations. Those scenarios show why an execution record can require more than a list of prices copied from the first report received. The document is a protocol reference, not evidence of how a particular broker displays its account statement. FIX Trading Community — Order State Changes, July 2020
A weighted calculation follows the actual sizes
Consider an entirely invented order filled for 30 units at 99.80 and 70 units at 100.20. The first execution contributes 2,994.00 in price-times-quantity value, and the second contributes 7,014.00. The total is 10,008.00 for 100 units, giving a quantity-weighted average of 100.08.
The unweighted mean of the two displayed prices is 100.00. That figure assigns equal importance to a 30-unit execution and a 70-unit execution, so it does not reproduce the illustrated total. The correct weighting answers a specific question: the average execution price per unit for those included fills.
It does not automatically answer the total-cost question. If the invented purchase also incurs a separately stated 5.00 charge, the cash outlay becomes 10,013.00 under that assumption. Dividing that amount by 100 gives 100.13 per unit including the assumed charge. A report should label those two figures separately rather than silently inserting a fee into an execution-price field.
Reconcile the execution set before comparing averages
Collect execution identifiers, quantities, prices, currency and any correction or cancellation records. Confirm that all the rows belong to the same intended order and that the total included quantity matches the quantity being summarised. Where a broker reports allocations separately, establish which allocation the average describes.
Keep enough decimal precision to reproduce the total before rounding a display value. Then reconcile separately stated fees, conversion charges and settlement amounts with the appropriate records. A difference between two interfaces may reflect their calculation scope, so establish that scope before calling either value wrong.
All quantities, prices and costs in the worked example are WFN assumptions. No market execution or broker-specific pricing policy is claimed. The field definition and calculation method were reviewed on 8 October 2026 to support clearer reading of execution reports.