How often should I change my logo?

Jay Conrad Levinson, author of the "Guerrilla Marketing" books, says you should plan to use a logo for at least twenty years. If that seems excessively long, note that you'll probably get tired of your company look much more quickly than anyone else.
Drastic change of a logo can wipe out brand equity built up at great cost over the years. This is a decision to make only with strong reasons, such as when the current logo no longer fits the business (for instance, the image of a slide rule when everyone now uses calculators and computers), when you want to emphasize new directions or when the logo was ill-chosen to begin with and you can now afford to remedy the problem.
In many cases, a designer can update a logo without producing a complete break from the current version. The continuity then maintains the recognizability you've had in the past.

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