We compare different tax incentive schemes for private R&D investments using a numerical model of R&D-investments and firm dynamics. We find that tax incentives that are based on the incremental annual spending increase firms’ R&D spending much more than tax incentives that are based on the level of R&D spending. However, incremental incentives also distort the allocation of R&D personnel across different firms much more than level-based tax incentives. This effect tends to lower aggregate output. We also find that whether the tax benefits are targeted to only profit-making firms, which pay corporate income tax, or given to all firms, does not make a big difference in terms of aggregate R&D spending or aggregate output.