We conduct a framed field experiment with 245 employed persons (no students) as subjects and a real tax, which is levied on the subjects' income from working in our real effort task. In our first three treatments, the net wage is constant but gross wages are subject to different constant marginal tax rates (0, 25%, 50%). It turns out that the effort is significantly higher under the tax than in the no tax treatment. Subjects perceive a too high net wage because they underestimate the tax. We conjecture that tax perception depends on the tax rate, the presentation of the tax and the experience subjects have with taxation. These conjectures are confirmed in four further treatments employing a direct and an indirect progressive tax scale. It turns out that simple flat taxes are particularly prone to being misperceived because their simplicity reduces the tax salience.