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.
Compare capacity and unused-time cost across departments or periods
The prompts above structure and check the model. This one lines departments, or periods, up side by side, so you can see where idle capacity cost is worst and whether it is getting better or worse. Run it once you have capacity figures for more than one department or period.
Capacity comparison across departments or periods
You are a cost accounting assistant helping a financial controller compare practical capacity and the cost of unused time across departments (or across periods). Work only from the data I give you. Do not invent any numbers. Show every formula before the value. If you cannot derive a figure, say so rather than estimate. I want to see where idle capacity cost is concentrated and which way it is moving, so I can direct attention and defend the number in the close review. Step 1. Take the resource groups (or periods) with, for each: total cost, practical capacity in minutes, and minutes actually consumed. Use only what I provide. Step 2. For each, compute the capacity cost rate (cost / practical capacity), unused minutes (practical minus consumed), and the cost of unused capacity, each as a formula before the value. Step 3. Put them side by side in one table: group | practical minutes | used % | unused cost | unused cost as % of total cost. Rank from worst to best utilisation. Step 4. Read the comparison. Name the one or two groups carrying the most unused-capacity cost, and, if I gave more than one period, whether each is improving or eroding. Step 5. Separate clearly what you calculated, what you assumed, and what you would flag for management attention. Do not recommend a headcount change or any action I have not asked for. Show every formula, present the comparison as a table, and reconcile used cost plus unused cost back to total cost for each group, flagging any discrepancy.
The comparison is only fair when every group is measured on the same practical-capacity basis. Change the allowance once and the ranking moves, which is exactly the discipline a real capacity model enforces.
Reconcile the cost model to the ledger at month end
The prompts above build and compare the model. This one closes the loop that the close review actually tests: does cost assigned to activities, plus the cost of unused capacity, tie back to what the general ledger says each department cost this month. What you walk away with is a reconciliation statement you can file with the close, with every gap sized, classified and either explained or flagged.
The month-end reconciliation prompt
You are a cost accounting assistant helping a financial controller reconcile a costing model to the general ledger at month end. Work only from the data I give you. Do not invent any numbers, rates or volumes. Show every formula before the value. If you cannot derive a figure from my data, say so rather than estimate. I want a reconciliation I can file with the close: model cost assigned plus unused-capacity cost, tied back to the ledger, department by department, with every difference sized and classified. My data: - Ledger cost per department for the month (from the trial balance or cost centre report): [paste] - Model inputs per department: total cost used by the model, practical capacity in minutes, capacity cost rate: [paste] - Cost assigned by the model to activities this month, per department: [paste] - Any known timing items (accruals, prepayments, one-off postings) I can confirm: [paste, or write "none confirmed"] Steps: 1. For each department, show the model identity as a formula: cost assigned to activities + cost of unused capacity = model total cost. Compute the unused-capacity cost line and flag any department where the identity does not hold. 2. Compare model total cost to ledger cost per department. Show the difference in currency and as a percentage of ledger cost. 3. Classify each difference using only what I gave you: TIMING (a confirmed accrual or one-off), SCOPE (a ledger line the model deliberately excludes; ask me rather than assume), RATE (the model used a cost figure that no longer matches the ledger), or UNEXPLAINED. Do not move a difference out of UNEXPLAINED without a confirmed reason. 4. Produce the reconciliation statement as one table: department | ledger cost | model assigned | unused capacity | model total | difference | classification | note. 5. Rank the UNEXPLAINED differences by size and state, for each, the single piece of data that would resolve it. 6. Separate clearly what you calculated, what I confirmed, and what remains open. End with every assumption in one block so I can correct it and have you rerun.
The classification discipline is the point: a difference parked as "timing" without a confirmed posting behind it is just an unexplained gap wearing a better name. The statement is only close-ready when the unexplained line is small enough to sign.
Make it a working model for the close pack
The prompts on this page produce a cost or capacity result in the chat. This add-on turns that result into a file you can audit and file with the close, an adjustable Excel model, a clean PDF, or a short deck. Paste it after the costing prompt once the numbers have run.
Now package this analysis into a deliverable I can audit and file with the close. Ask me which format I want, or default to Excel: - EXCEL: a working model, not a picture of one. Put the inputs (department or resource-group cost, practical capacity minutes, minutes consumed, activity volumes and any rates) on one clearly marked input sheet, and drive every result, capacity cost rate, unused-capacity cost, cost assigned to each activity, with live formulas that reference those inputs, so when I change a figure everything updates. Add a summary sheet with the reconciliation (assigned plus unused equals total) and, if the tool allows, a chart. Label every assumption cell. - PDF: a clean, close-ready report, title, one-paragraph summary, the capacity or activity cost table, the reconciliation, one chart, and an assumptions appendix. No chat formatting. - PPT: 5 to 7 slides, the question, the method in one slide, the capacity or cost result, where unused cost sits, the point to raise with management, next steps. Rules for the deliverable: - Keep all inputs adjustable and visible; never hard-code a result I might want to change. - Carry every reconciliation through so assigned cost plus unused cost ties back to total cost. - Carry through every assumption and label illustrative figures as illustrative. - Add a discreet footer or last-slide credit line, small and unobtrusive, exactly as written below. Credit line to embed (use verbatim, in the document footer or final slide): "Model scaffolding based on the controller costing prompts from costandprofitability.com/ai-costing-prompts/for-controllers" Keep it to one small line; it should read as a quiet source note, not an advertisement.
The credit line is deliberately modest, a source note rather than a watermark, so the file is comfortable to file with the close while the method stays traceable to where it came from.
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.
Related
Proof
A distributor in New Zealand. €1.335M of cost-to-serve made visible, then halved, and 830 loss-making customers brought down to 295.
Read the case study →Who you would be talking to
Miguel Guimarães, Founding Partner
Cost and profitability practitioner for 25+ years. Presented the Damco cost-to-serve case at Managing for Profit (Amsterdam RAI, December 2009), on the same programme as Robert S. Kaplan.
Call +351 910 313 731
