The FAST Standard is published openly and regularly revised by the FAST Standard Organisation. The Signatories to the FAST Standard believe financial models must be as simple as possible, but no simpler. Any model that is unnecessarily complicated is not good. Without simplicity supported by rigorous structure a financial model will be poorly suited to its sole purpose – supporting informed business decisions.

The FAST Philosophy

The Standard advocates a philosophy of good financial model design rules founded on the acronym FAST: flexible, appropriate, structured, and transparent. It advocates transparent model structure and clear, crisp modelling style. See section The Fast Acronym on page 7, for details on each of these fundamental design priorities.

The FAST Standard is primarily concerned with good spreadsheet design. While its remit does not extend to the management and control environment in which spreadsheets are used (such as back-up, version control and testing), modellers using the Standard are encouraged to consider these important aspects of the business environment when building and deploying their models.

The Standard has been developed from the experience of industry practitioners who have learned simple techniques to replace overly-clever ‘good ideas’ that proved bad in practice over time. It documents a skilled craft that is functional within the realities of the business environment. As a minimum objective, models must be free of fundamental omissions and logical errors, and this outcome must be achieved under short lead times. However, a good model must achieve more than this minimum standard. It must be easily used and reviewed by others and readily adaptable as circumstances change.

The FAST Standard speaks predominantly about outcomes, i.e what the final model should look like. It dwells little on the trade-craft of executing spreadsheet models, with specifics related to Microsoft Excel-based execution. For instance, it does not detail the use of recommended Excel keystrokes or so-called shortcut keys – vastly superior to using a mouse in almost all circumstances – on which the FAST Standard relies.

However, no set of design rules can be entirely divorced from the manufacturing environment in which the product must be built. Many of the design rules are expressly recommended because of the strengths and weaknesses of the Microsoft Excel modelling environment, providing designs that take advantage of the environment’s strengths and mitigating its weaknesses. Recommending design that takes advantage of efficient and error-reducing construction techniques is one of the prime objectives of the FAST Standard.

Finally, the FAST Standard presumes the reader has a good understanding of Excel; this is not a ‘how to’ document, but a professional Standard supported by expert modellers.


Model design and modelling techniques must allow models to be both flexible in the immediate term and adaptable in the longer term. Models must allow users to run scenarios and sensitivities and make modifications over an extended period as new information becomes available — even by different modellers. A flexible model is not an all-singing, all-dancing template model with an option switch for every eventuality. Flexibility is born of simplicity.


Models must reflect key business assumptions directly and faithfully without being over-built or cluttered with unnecessary detail. The modeller must not lose sight of what a model is: a good representation of reality, not reality itself. Spurious precision is distracting, verging on dangerous, particularly when it is unbalanced. For example, over-specifying tax assumptions may lead to an expectation that all elements of the model are equally certain and, for example, lead to a false impression, if the revenue forecast is essentially guesswork. An overly precise base case only serves to drown analytically more important scenario-based risk analysis and likely ensures the model is incapable of conducting Monte Carlo analyses practically.


Rigorous consistency in model layout and organization is essential to retain a model’s logical integrity over time, particularly as a model’s author may change. A consistent approach to structuring workbooks, worksheets and formulas saves time when building, learning, or maintaining the model


Models must rely on simple, clear formulas that can be understood by other modellers and non-modellers alike. Confidence in a financial model’s integrity can only be assured with clarity of logic structure and layout. Many recommendations that enhance transparency also increase the flexibility of the model to be adapted over time and make it more easily reviewed. Fundamental to supporting each of these aims is the root definition of the term analysis– the concept of ‘breaking things up’. This theme must be applied at different levels of model design: tactically in forming short, simple formulas; functionally to separate timing, escalation, and monetary calculations; and structurally at the level of worksheet purpose.

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