The OECD R&D Tax Incentives database presents OECD time-series indicators of implied tax subsidy rates on R&D expenditures by firm size and profitability scenario for OECD member countries and other major economies, drawing on data collected in the OECD R&D tax incentives surveys since 2007. Implied R&D tax subsidy rates are defined as 1 minus the B-Index, a measure of the before-tax income needed by a “representative” firm to break even on one additional monetary unit of R&D outlay (Warda, 2001; OECD, 2023). The more generous the tax provisions for R&D, the lower the before-tax breakeven economic return required by firms and the higher the implied marginal R&D tax subsidy. The OECD time-series estimates of implied R&D tax subsidy rates is based on headline tax credit and allowance rates. Due to limited historical data availability, the estimates are not adjusted for provisions that bound the tax benefits received by firms (e.g. ceilings, thresholds). They therefore provide an upper bound for the marginal tax subsidy implied by R&D tax relief measures at central government level across countries over time. OECD (2019) provides a practical guide to using the OECD R&D Tax Incentives database, describing the R&D tax incentive time series data and highlighting their potential for internationally comparative work through descriptive indicators and econometric analysis.