AI costing prompts · By role
AI costing prompts for the financial controller
You own the cost model and you own the close, which means you also own every number a director questions in the meeting after. AI can take real work off your desk, but only if it never quietly invents a figure you then have to defend. These prompts are written to keep the model honest, speed the close, and leave you with outputs you can stand behind.
In short
As a controller, use AI to structure, draft and check costing work, never to supply numbers it was not given. The prompts below help you frame a TDABC model, sanity-test capacity and unused time, and turn cost results into board-ready commentary. Each one forces the model to work only from your data, flag every assumption, and show its formulas before any result, so what reaches the close is traceable.
What a controller should and should not ask AI to do
AI is genuinely useful where the task is structural rather than factual: laying out cost pools and drivers in a consistent format, drafting the time equations from process steps you describe, writing first-pass variance commentary, and converting a finished result into plain board language. It is also a fast second reader, catching where a subtotal does not foot or where a driver is double-counted. In all of these, you supply the numbers and the judgement; the model supplies structure and speed.
Where it is risky is precisely where it is tempting: asking it to "estimate" a rate, "assume a typical" headcount, or "fill in" a missing volume. A language model will produce a confident, plausible figure that has no basis in your ledger, and once it lands in a model it is hard to trace back out. Treat any number the model offers that you did not give it as wrong until proven otherwise. Keep allocation policy, capacity assumptions and the final sign-off in your hands, not the model's.
Three prompts to start with
1. Frame a defensible TDABC model
Use this to turn a messy set of cost lines and process notes into a clean, auditable model structure. It pairs with the full method on the build a TDABC model page.
You are a cost accounting assistant helping a financial controller structure a time-driven activity-based costing (TDABC) model. Work only from the data I give you. Do not invent any numbers, rates or volumes. List every assumption you make, and where a figure is missing label it DATA MISSING and tell me what you need. My data: - Departments and their total cost for the period: [paste, e.g. Order Desk 120,000; Warehouse 85,000] - Practical capacity per department (minutes available): [paste] - Activities each department performs: [paste] - Volume of each activity in the period: [paste] Steps: 1. For each department, show the capacity cost rate as a formula (department cost / practical capacity minutes) before computing it. 2. List the activities and ask me for the time-per-unit for any I have not provided. Do not estimate them. 3. Build the time equation for each activity from the components I supply. 4. Show the cost assigned to each activity as a formula, then the value. 5. Reconcile total cost assigned back to the department cost I gave you and flag any difference.
2. Test capacity and the cost of unused time
The controller's quiet question is always "what are we paying for that we do not use." This prompt isolates idle capacity cleanly. See also capacity cost.
You are helping a financial controller analyse practical capacity and unused capacity cost. Work only from the data I give you. Do not invent any numbers. Show each formula before the value. If you cannot derive a figure from my data, say so rather than estimate. My data: - Theoretical capacity (total paid minutes) per resource group: [paste] - Practical capacity (usable minutes after allowances) per resource group: [paste] - Minutes actually consumed by activities this period: [paste] - Total cost per resource group: [paste] Steps: 1. Show the capacity cost rate per resource group (cost / practical capacity) as a formula, then the value. 2. Compute used minutes vs practical capacity and show the unused minutes. 3. Translate unused minutes into a cost of unused capacity using the rate. 4. Separate clearly: what you calculated, what you assumed, and what you would flag for management attention. 5. Check that used cost plus unused cost equals total cost and flag any discrepancy.
3. Turn cost results into close-ready commentary
When the numbers are signed off, this drafts the narrative for the pack without overstating anything. It links to board reporting.
You are drafting management commentary for a financial controller's close pack. Work only from the figures I give you. Do not invent or extrapolate any numbers. If a movement needs an explanation I have not provided, ask me rather than guess the cause. My data: - Cost by activity or department, this period vs prior period vs budget: [paste] - Any known drivers of movement I can confirm: [paste] Steps: 1. List the three largest variances by value and show the variance as a formula (actual minus comparison). 2. For each, state only the size and direction of the movement; do not attribute a cause unless I gave you one. 3. Where a cause is unknown, write "cause to confirm" rather than inventing one. 4. Draft a short, plain-language paragraph suitable for a board pack. 5. Keep every number consistent with my data and flag any total that does not reconcile.
The one rule
Work only from the data I give you. Do not invent any numbers, rates or volumes. Label anything missing as DATA MISSING and tell me what you need.
This single line is the difference between a useful draft and a liability. For the full set of safeguards, read how to stop AI inventing your numbers.
From a faster close to a model you can trust
Prompts will speed your drafting and tighten your checks, but they cannot reconcile your data or set your allocation policy. That is the work we do with controllers every week: a model built on your reconciled ledger, with capacity and drivers you can defend line by line. If you want the model itself to be sound, not just the commentary around it, start with a health check.