# Driver Based Budget Builder

> Builds a monthly budget from real volume, price, and department cost growth drivers via a bundled calculator, phased across the year, instead of the "last year plus X%" shortcut that hides every real assumption behind one blended growth rate. Use whenever the user is building an annual or departmental budget, needs a phased monthly plan rather than a single annual number, or has a budget built as a flat percentage increase over last year with no driver logic behind it.

- Skill: `natan-mohart/driver-based-budget-builder` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add natan-mohart/driver-based-budget-builder`
- Raw SKILL.md: https://api.skillmd.com/api/skills/natan-mohart/driver-based-budget-builder/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Marketing & Growth
- Author: Natan-Mohart (https://skillmd.com/u/natan-mohart)
- Updated: 2026-09-21
- Page: https://skillmd.com/skills/natan-mohart/driver-based-budget-builder

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# Driver-Based Budget Builder

## When to use
Use whenever a budget needs to be built or rebuilt from real drivers rather than "take last year and add X%" — a shortcut that hides whether growth is coming from volume, price, or something else, and applies the same blended assumption to every department regardless of what actually drives its cost.

## What it does
Builds a phased, monthly budget from explicit revenue drivers (starting volume, volume growth rate, price, and timed price changes) and department-level cost growth rates via a bundled calculator, producing a full monthly build with revenue, opex by month, and EBITDA, rather than a single annual figure with no visibility into how it's phased.

## Method
1. **Decompose revenue into volume and price separately**, never a single blended revenue growth rate. State the starting volume, the monthly volume growth rate, the starting price, and any planned price changes with their timing (many businesses change price once a year, not continuously — model it as a discrete jump on the right month, not smoothed across twelve months).
2. **Build cost by department, not one company-wide opex line.** Each department has a different natural growth rate: R&D might scale with headcount plans, G&A might grow slower than revenue, sales and marketing might scale with the pipeline the growth target requires.
3. **State each department's monthly growth rate explicitly**, tied to a real driver (headcount additions, planned tooling costs, marketing spend as a percent of pipeline target) rather than a copied-forward percentage.
4. **Run the bundled calculator** (`scripts/driver_budget.py`) to get the full monthly build: units, price, revenue, total opex, and EBITDA for every month of the year.
5. **Check the phased shape, not just the annual total.** A budget that's flat month to month rarely matches how a real business actually grows — look for whether the monthly progression makes sense (seasonality, a price increase landing on a specific month, ramping costs ahead of a launch).
6. **Sanity-check the full-year EBITDA margin against what's actually achievable** — a budget that implies a margin far outside historical range or peer benchmark needs its drivers revisited, not just accepted because the formula produced it.
7. **Feed this bottom-up build into annual-operating-plan** to reconcile against any top-down target leadership has in mind, rather than treating this build as the final published budget on its own.

## Inputs
- Starting volume/units and monthly volume growth rate
- Starting price and any planned price changes with timing
- Department list with starting monthly cost and monthly growth rate per department
- Config saved as JSON matching the format documented at the top of `scripts/driver_budget.py`

## Output format
Full monthly table: units, price, revenue, total opex, and EBITDA for every month; full-year totals; full-year EBITDA margin.

## Example
A budget built as "last year's $3.2M revenue plus 20%" gives one number with no way to check if it's realistic. Rebuilding from drivers, 1,000 starting units growing 4% monthly with a 3% price increase in month 7, produces $3.82M with visibility into exactly when and why revenue accelerates, plus a full monthly opex build showing the business runs at a -68% EBITDA margin for the year, a number worth challenging on the cost side before the budget is finalized, not something a single blended annual figure would have surfaced.

## Common pitfalls
- Building revenue as one blended growth rate instead of separating volume and price, which hides which lever is actually doing the work.
- Applying the same growth rate to every department instead of driver-based rates per department.
- Publishing only the annual total without the monthly phasing, missing whether the shape of the year actually makes sense.