We investigate whether the optimal income tax model of Mirrlees (1971) can reproduce the empirically observed increasing average tax rates. We give a necessary condition and exhibit two examples where the optimal average tax rates are increasing.
Hindriks, J., Lehmann, E., & Parmentier, A. (2006). Optimal income taxation and the shape of average tax rates. Economics Bulletin, 8(2), 1-6. https://hdl.handle.net/2078.5/250125 (Original work published 2006)