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A published price index describes a specified basket and method. Your planning worksheet may contain a different mix of expenses. Neither difference makes the official measure wrong; it changes the question you are trying to answer.
Identify the spending categories
Separate recurring housing, food, transport and other obligations in your own records. Decide which categories matter to the scenario being modelled and make the starting amounts visible.
Show the assumptions explicitly
In a fictional three-category budget, assign weights of 50%, 30% and 20%, and hypothetical annual price changes of 5%, 8% and 3%. Their weighted change is 5.5%. These invented numbers are not current Indian inflation data or a forecast.
The calculation is useful because a reader can see how the result changes when a category’s weight or assumption changes. Do not label a personal scenario as an official index.
Test uncertainty rather than hiding it
Try different assumptions for the categories that matter most. Identify a cost that might change discontinuously, rather than smoothly, and keep it separate when appropriate.
Review the worksheet against actual spending over time. A model should be updated because the evidence or purpose changed, not because a precise figure makes the plan look more convincing.
This is an original planning illustration. It complements our cash-flow calendar by examining spending assumptions rather than forecasting market returns or prescribing a personal retirement budget.
