Wealth transfer taxes are important instruments to counter increasing wealth inequality. Yet, inter-generational business transfers, whose distribution is particularly concentrated at the top, are inherently difficult to tax. This is due to preferential tax treatments in many countries and sophisticated tax avoidance strategies by business owners. We analyze how business transfers react to anticipated changes in such preferential tax treatment using German administrative gift tax return data. We find strong timing responses of business transfers to expected tax changes, particularly for large transfers of business wealth. We further estimate that the amount of foregone gift tax revenue due to timing responses is up to 2.8 times the size of actual annual inheritance and gift tax revenue.