> For the complete documentation index, see [llms.txt](https://docs.dataloy.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.dataloy.com/release-8.31/voyage-management-system/step-by-step-guides/voyages/maintain-voyages/voyage-analysis/deviation-calculation.md).
# Deviation Calculation
This page provides a detailed explanation of a Voyage Function - Deviation calculation.
The deviation calculation function offers a comprehensive analysis of the difference between the current voyage and the same voyage as if it were direct — from the ballast port to the last port call.
This function is particularly useful when freight rates are low, voyages must adhere to strict schedules, or deviations are required for compliance. It helps determine whether an additional detour can generate enough extra revenue to offset the added distance, time, emissions, and fuel costs.
Figure 1. Deviation Calculation modal.
Figure 1 shows the Deviation Calculation window, comparing the current voyage results (in the Loaded column) with a hypothetical direct voyage (in the Direct column). The Variance column highlights the differences between the two. By clicking Open Direct Voyage, users can review the direct route’s details (Figure 2). In this example, the detour with cargo generates higher revenue, making it a more favourable option.
#### Prerequisites:
* The Deviation Calculation function is available only for **Estimate Voyages**.
Figure 2. Direct Voyage from the Deviation modal.
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