Measure costs when only part of an intended trade completes

When an order completes only partly, report the filled quantity, the actual spending or proceeds for that quantity, the separate charges incurred, and the unfilled remainder. The unfilled portion is not automatically a loss or a zero-priced fill.

A partial purchase example

Suppose the hypothetical goal is to acquire 100 tokens. So far, 40 tokens have filled for 198 stablecoins, with two stablecoins of separately paid charges. Realized all-in acquisition cost is 200 / 40 = five stablecoins per acquired token.

The completion ratio is 40%. Sixty tokens remain unacquired. Dividing 200 by the full intended 100 would produce a false two-stablecoin acquisition price for tokens that were never bought.

Different execution systems allow different outcomes

CoW Protocol's explanation of partial fills illustrates an order that can execute portions over time. Do not assume this behavior applies to every ordinary atomic swap; the submitted order's rules determine what completion states are possible.

Keep remaining exposure visible

The unchanged input balance may still be available for the unfilled portion, but its future buying power can change. A report can describe that exposure without inventing an execution loss on an unexecuted trade.

If the task is later abandoned, preserve the realized filled-price calculation and state the final completion percentage. If it continues, include later fills and fees in the aggregate totals rather than overwriting the original partial result.

Comparing two methods requires comparable completion goals and deadlines. One method that fills only the easiest 10% may show a lower average cost than one that completes everything. Show both completion and cost before assigning a performance ranking. Where costs cover the entire order setup, disclose how they are allocated to completed fills rather than assuming that unfilled portions absorbed them.