September is the first month Bill pays for everything himself. Rent, food, transport, utilities. He modelled this in May. He knows the numbers. What he did not model was the friction of a new city: the extra taxi because he did not yet know the bus route, the supermarket that was more expensive, the dinner with new colleagues that he did not want to decline.
He runs the variance at the end of September.
Budget: 1,215 in outflows, 1,400 in income, 185 surplus. What actually happened: outflows of 1,490, income of 1,400, deficit of 90. The variance is negative 275 euro against the plan.
Budget variance analysis measures the difference between plan and reality. A negative variance in the first month of a new configuration is not evidence that the model is broken. It is evidence that the model was built without the data that only experience provides.
Bill adjusts his miscellaneous budget from 80 to 130 and his food budget from 250 to 280. The new baseline surplus is 105 euro per month. He accepts it.
The tip
A first-month variance is information, not failure. The budget built before the experience is a hypothesis. The variance tells you what the hypothesis missed. Update the model and move forward.
Budget variance, September 2025: planned surplus 185, actual deficit -90. Variance: -275. Adjusted monthly surplus from October: 105. The model was not wrong. It was incomplete.
Bill is 25. Every episode, we read his personal ledger through accounting eyes. / FY 2025 ledger