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Ten Financial Modeling Commandments


A financial model is one of the essential project documents that is used by all stakeholders involved in the life of any project or deal. A financial model is mainly built in Excel. Like any other project document, the financial model should be transparent and readable. Unlike a Word document, it can be made flexible. This allows you to make changes as you review the document. In essence, a good financial model is an informative document. However, it can also be a tool for better decision making.

In life, I follow these three simple rules: "Good thoughts, good words, and good deeds." For my financial models, I follow these ten rules.

1. Thou Shalt Keep it Simple

It is horrible to receive a comment from a user and even worse from an auditor saying that your model is complex and heavy. However, keep in mind that simplicity is a relative term and must be considered in connection with the level of knowledge of the recipient. For example, a standard financial model might be labeled as complex by someone who has little knowledge of Excel and financial modeling. On the other hand, the same model reviewed by a spreadsheet engineer might be labeled as stupid.


2. Thou Shalt Separate Inputs From Calculations And Results

This is more like a Feng Shui exercise than financial modeling. For transparency and ease of access to model assumptions, dedicate a separate worksheet or a separate place on a single model worksheet for your assumptions. Also, categorize your assumptions by type.

3. Thou Shalt Not Hard-Code Inputs Within Formulas

This is like an environmental issue in financial models. It’s the same dilemma as why some people continue to throw their trash on the ground? Not that the input that you are hard-coding is trash but with hard-coding inside the formula, you are treating that piece of information as trash and burying it without a headstone or nameplate!


4. Thou Shalt Use Color Codes

Use a consistent color scheme to mark different types of cells and data.

Again, keep it simple. You don't want to overdo it with too many colors or crazy, over-the-top formatting.

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5. Thou Shalt Avoid Long Formulas

Use the Feng Shui rule of thumb of financial models: “Do not write a formula longer than your thumb."

6. Thou Shalt Build In Error Checks

Everything might work perfectly fine in your base case but once you change any inputs, something might go wrong and you should be notified. Let me tell you a secret, I consider my models as my babies and the built-in checks as the baby monitor. So, once something is wrong in one part of my model, one of the checks will tell me that the baby needs attention.

7. Thou Shalt Include Sensitivity and Scenario Analysis

You need to do further modeling so that your model can start talking alternative future scenarios. Your model should be smart and should not suffice to a single worldview.


8. Thou Shalt Insert Summary Charts and Tables

The typical user should just validate and make changes to the inputs that you have clearly defined in your spreadsheet and then go to a summary sheet to see the main results. In this sheet, you can unleash your creativity and come up with dynamic and beautiful charts and tables.

9. Thou Shalt Avoid Circular References

They should have named this phenomenon “vicious cycle”. That’s what it does to a financial model.

10. Thou Shalt Not Be Selfish

Neglecting usability or user friendliness in a financial model is a costly mistake. A financial model should be easy to read and manipulate for users.


This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2018 Hedieh Kianyfard

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