AI costing prompts · By role
AI costing prompts for the FP&A analyst
You live in the gap between the forecast you submitted and the actuals that arrive to contradict it, and most of your week goes on rebuilding, reconciling and explaining. AI can take real friction out of forecasting and variance work and cut the manual errors that creep in at speed, as long as it never substitutes its own numbers for your model's. These prompts add rigour, not guesswork.
In short
Use AI to structure forecasts faster, frame scenarios cleanly, and pull a tidy variance story out of a wide actuals file, all without letting it invent a single figure. The prompts below help you build a driver-based forecast, run scenarios you can defend, and explain variances against plan with the cause separated from the noise. Each one keeps the model working only from your data and forces it to show every formula before any result.
What an FP&A analyst should and should not ask AI to do
AI is a strong ally for the mechanical and structural parts of the job. It can lay out a driver-based forecast from the relationships you describe, generate consistent scenario variants once you give it the base, draft variance commentary that distinguishes volume from rate, and check a long actuals file for the slips that cause rework: a sign flipped, a subtotal that does not foot, a period mislabelled. These are exactly the tasks where speed introduces errors, so a careful second pass pays for itself.
It becomes risky the moment you let it produce inputs. Asking AI to "assume a growth rate," "estimate seasonality," or "fill the gaps in this forecast" yields plausible numbers with no link to your business, and a forecast built partly on invention is worse than one with honest gaps. Keep the drivers, the assumptions and the judgement about what is reasonable in your hands. Let AI accelerate the build and audit your arithmetic, not author the future.
Three prompts to start with
1. Build a driver-based forecast
Use this to structure a forecast around real drivers rather than last year plus a percentage. It builds on the budgeting and forecasting page.
You are an FP&A assistant helping build a driver-based forecast. Work only from the data I give you. Do not invent any rates, volumes or growth assumptions. List every assumption, and label anything missing as DATA MISSING with what you need from me. My data: - Cost or revenue lines and their driver (for example, cost scales with order volume): [paste] - Historical values for each driver and each line: [paste] - The forecast drivers I am giving you for the period ahead: [paste] Steps: 1. For each line, show the unit relationship (line value / driver) from history as a formula, then the value. 2. Apply only the forecast drivers I supplied; do not assume any I did not give. 3. Show each forecast line as a formula before the number. 4. Separate clearly: what you calculated, what I assumed via the drivers, and any concern you would flag. 5. Check that the forecast lines sum to the total and flag any discrepancy.
2. Run defensible scenarios
Generate consistent best, base and downside cases without smuggling in invented inputs. See budgeting and forecasting.
You are helping an FP&A analyst build three scenarios from one base forecast. Work only from the data I give you. Do not invent the scenario inputs; use only the changes I specify. Show each calculation as a formula before the value. My data: - Base forecast by line: [paste] - The specific changes for each scenario (for example, downside = order volume -10%): [paste for base, upside, downside] Steps: 1. Restate the base so I can confirm it. 2. For each scenario, apply only the changes I specified and show the affected lines as formulas. 3. Present the three scenarios side by side with the delta to base for each. 4. State the single assumption each scenario most depends on. 5. Check each scenario foots to its total and flag any that does not.
3. Explain variances against plan
Pull a clean volume-versus-rate story out of a wide actuals file. Links to board reporting.
You are helping an FP&A analyst explain variances of actuals against plan. Work only from the figures I give you. Do not invent causes or numbers. If a variance needs an explanation I have not provided, write "cause to confirm". My data: - Lines with actual, plan, and where available the volume and rate behind each: [paste] Steps: 1. Compute each variance as a formula (actual minus plan) and rank by absolute value. 2. Where I gave volume and rate, split the variance into a volume effect and a rate effect, each as a formula. 3. For the top three, draft one plain sentence each, attributing a cause only where I confirmed it. 4. Separate clearly: what you calculated, what I confirmed, and what is unexplained. 5. Check that the individual variances reconcile to the total variance and flag any gap.
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.
A forecast built on an invented input is harder to fix than one with an honest gap. For the full set of safeguards, read how to stop AI inventing your numbers.
Faster forecasts rest on a sound cost base
Prompts will speed your build and tighten your variance work, but the quality of any forecast depends on the cost model feeding it. Where costs are allocated badly, even a perfect forecast forecasts the wrong thing. We help finance teams put a defensible cost and profitability model under the planning process, so the drivers you forecast on are the ones that actually move the business. Start by seeing where your current model stands.