write-financial-model

name	write-financial-model
description	Use when building a three-statement financial model for a company or business unit
source	McKinsey "Valuation: Measuring and Managing the Value of Companies" (7th ed.); Macabacus financial modeling standards; BIWS (Breaking Into Wall Street) modeling curriculum
tags	["finance","corporate","financial-modeling","three-statement","forecasting","sensitivity"]
verified	true

Write Financial Model

Construct an integrated three-statement financial model linking income statement, balance sheet, and cash flow statement.

Why This Is Best Practice

Adopted by: Investment banks (Goldman Sachs, JP Morgan), management consulting firms (McKinsey, Bain), corporate finance teams at Fortune 500 companies Impact: McKinsey "Valuation" research demonstrates that integrated three-statement models reduce forecasting errors by forcing accounting consistency; broken links between statements are the primary source of model errors in practice.

Why best: Three-statement integration ensures that every assumption flows consistently through all financial statements. A model where cash flow does not reconcile to the balance sheet is fundamentally unreliable. Sensitivity analysis built into the structure allows real-time scenario toggling without rebuilding the model.

Steps

1. Set up model architecture — Separate tabs: Assumptions, Income Statement, Balance Sheet, Cash Flow Statement, Valuation, Sensitivity; color-code: blue = hardcoded inputs, black = formulas, green = links from other sheets.
2. Build the income statement — Start with revenue drivers (volume × price or segment-level); model COGS, gross margin, OpEx line items, EBITDA, D&A, EBIT, interest expense, taxes, net income.
3. Model the balance sheet — Link retained earnings to net income; model working capital (AR = DSO × Revenue / 365; Inventory = DIO × COGS / 365; AP = DPO × COGS / 365); model PP&E schedule (beginning + CapEx − D&A = ending).
4. Build the cash flow statement — Use indirect method: start with net income; add back D&A; adjust for working capital changes; subtract CapEx; add/subtract financing activities; ending cash must equal balance sheet cash.
5. Create the debt and interest schedule — Model revolving credit, term loans, and new issuances; interest expense feeds back to income statement; this is the circular reference — use iterative calculation or break with prior-period average balance.
6. Build a scenarios tab — Define at minimum three scenarios (base, upside, downside) by toggling revenue growth, margins, and CapEx assumptions; use INDEX-MATCH or scenario manager.
7. Add sensitivity tables — Two-way data tables for key outputs (EV, equity value, EPS) across revenue growth and EBITDA margin; mandatory before any presentation.
8. Audit and stress-test — Run error checks: does cash flow match balance sheet delta? Is retained earnings roll-forward correct? Run the downside scenario to confirm the model does not break.

Rules

• Every hardcoded number must live in the Assumptions tab only; never bury inputs inside formulas.
• The balance sheet must balance (Assets = Liabilities + Equity) in every period; this is a non-negotiable integrity check.
• Avoid circular references where possible; if required (interest on average debt), enable iterative calculations with maximum iterations set to 100.
• Label units (thousands, millions) prominently; unit errors are a leading cause of model disasters.
• Protect formula cells; only input cells should be editable in shared models.

Examples

SaaS company model: Revenue drivers = ARR × net revenue retention + new ARR bookings. Gross margin = 72% (stable). S&M = 40% of revenue declining to 30% over 5 years as CAC payback improves. R&D = 20% of revenue. G&A = 10% declining to 7%. EBITDA margin: year 1 = 2%, year 5 = 23%. D&A = 5% of revenue. CapEx = 3%. Working capital: DSO 45 days, DPO 30 days, no inventory.

Common Mistakes

• Hard-coding calculated values — Never paste values over formulas; future scenario changes will silently break the model.
• Ignoring minority interest and non-controlling stakes — These affect equity value; model them explicitly if material.
• Building a model no one else can audit — Overcomplicated formulas defeat the purpose; if you cannot explain every cell, refactor.

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Finance disclaimer: This skill encodes professional best practices for educational purposes. It is not financial advice. Consult a licensed financial advisor before making investment decisions.