"Material costs are $40,000 over budget" doesn't say what to fix. Did we pay more per unit, use more per product, make more products, or make a different mix? Variance analysis splits the total gap into those pieces.
Where it comes from
Variance analysis is a core management-accounting method, taught with standard costing and flexible budgets in ACCA and CMA courses. The basic split for a cost:
| Variance | Formula | Asks |
|---|---|---|
| Price | (actual price − standard price) × actual quantity | Did we pay more per unit? |
| Usage | (actual quantity − standard quantity for actual output) × standard price | Did we use more per product? |
| Volume | flexible budget − original budget | Did we make or sell more than planned? |
| Mix | Change in the blend of products at standard margins | Did we sell a different blend? |
The flexible budget is the key step. It restates the budget at the volume you actually made, so a busy month doesn't look like overspending.
How a bot helps
The arithmetic is mechanical and a bot does it reliably if it's given the standards, the volumes and the actuals. It should show every formula with its numbers, and check that the pieces add back to the total gap.
The explanation isn't mechanical. A price variance could be a supplier increase, a rush order, or a different grade of steel. A bot can propose candidates from purchase records. A person who knows the business confirms which.
On the bots' own work
Token spend is a budget too. Split a bot team's over-spend into price (a model's rate changed), volume (more tasks) and usage (more tokens per task). Only the last one is a bot design problem. See cost and model choice.
When to use it
Monthly, after close, for the lines over a threshold you set in advance. Medium rigor: the numbers are quick, the explanations take a conversation.
Where bots differ
A bot will happily explain a variance with a plausible story. Make it label each explanation: measured from records, inferred, or a guess for a person to confirm.
Sources: ACCA: moving up from F5 to P5 (variances and flexible budgets).
Back to Engineering tools for bots.
Short outline
Variance analysis: short outline
What it's for
Variance analysis splits the gap between budget and actual into price, usage, volume and mix, using a flexible budget, so each piece points to something that can be fixed or explained.
Columns
| Column | What goes in it |
|---|---|
| Line | The budget line being analyzed |
| Budget | Original budget amount |
| Flexible budget | Budget restated at actual volume |
| Actual | Actual amount for the period |
| Variance | Price, usage, volume or mix |
| Amount | The variance, favorable or unfavorable, with its formula and numbers |
| Explanation | The business reason |
| Basis | Measured, inferred or guess |
| Action and owner | What happens next, or "none: explained" |
Steps, each with its "done when"
- Pick the lines and the threshold. Done when the lines to analyze and the size of variance worth explaining are set before looking at the results.
- Build the flexible budget. Done when each line is restated at actual volume, with the volume source cited.
- Split each gap into variances. Done when each variance shows its formula and numbers, and the pieces add back to the total gap.
- Explain each variance over the threshold. Done when each has an explanation labeled measured, inferred or guess, and every guess has a person to confirm it.
- Assign actions. Done when each unfavorable variance that isn't a one-off has an owner and a next step.
Common mistakes
- Comparing actual to the original budget instead of the flexible budget.
- Variances that don't add back to the total gap.
- A plausible story written down as the explanation without checking records.
- Explaining every small variance instead of the ones over the threshold.