A deviation from the budget may depend on quantities sold, prices, composition of purchases or execution times. The comparison between two totals signals a difference, but leaves the decision open. It is necessary to understand which component has modified the result and if it can repeat itself.
I propose to break down the main variations using a few understandable categories. A higher cost may result from increased activity or a different unit price. The meaning changes: in the first case it must be compared with the additional work; in the second, with the conditions of purchase.
Let's imagine a store that spends more than expected on deliveries. An increase in online orders could explain some of the variation. Repeated deliveries to the same recipient could explain the rest. The two causes require different organizational interventions.
The reading should end with a decision and a new hypothesis to be verified. Registering the cause avoids repeating generic explanations every month. A budget remains useful when it helps to recognize what has changed and to correct subsequent predictions.