Using a panel of German income tax accounting data from taxpayers with no business income (employees), we find a negative relationship between tax preparation expenses and tax liabilities. However, preparation expenses are shown to exceed estimated tax savings. Specifically, one additional Euro spent on preparation yields an estimated tax savings of 72 cents in an OLS regression and 24 cents in a fixed effects regression. In addition, we observe substantial heterogeneity in tax savings among income groups, but even if we account for long-term tax savings, tax liability reductions exceed tax preparation expenses only for the highest income quintile. In all other income quintiles, average preparation expenses exceed the estimated tax and time savings. Based on these results, we also examine whether other specific benefits affect an individual's decision to purchase tax preparation services, and the results indicate the importance of the benefits of coping with complexity and reduced uncertainty. Overall, our findings illustrate that the current tax compliance process violates at least two of Adam Smith's principles of taxation, taxes are neither certain nor fair.L'incidence des frais de pr eparation des d eclarations fiscales sur les salari es : donn ees allemandes R ESUM E A partir d'un ensemble de donn ees allemandes relatives a la comptabilisation de l'impôt sur le revenu de contribuables salari es (ne recevant pas de revenu d'entreprise), les auteurs notent l'existence d'une relation n egative entre les frais de pr eparation des d eclarations fiscales et les obligations fiscales. Ils constatent toutefois que les frais de pr eparation exc edent les economies fiscales estim ees. Plus pr ecis ement, un euro suppl ementaire d evolu a la pr eparation des d eclarations fiscales produit une economie fiscale estimative de 72 cents, selon une r egression des MCO, et de 24 cents, selon une r egression a effets fixes. De plus, les auteurs observent une h et erog en eit e importante des economies fiscales entre les tranches de revenu, mais même lorsqu'ils tiennent compte des economies fiscales a long terme, les r eductions des impôts a payer exc edent les frais de pr eparation des d eclarations seulement pour le quintile de revenu sup erieur. Dans tous les autres quintiles de revenu, les frais de pr eparation moyens exc edent les economies estimatives d'impôt et de temps.