That's a believable number. But I also imagine that the curve flattens considerably before topping out: Sweden probably wouldn't get a lot of additional revenue

That's a believable number. But I also imagine that the curve flattens considerably before topping out: Sweden probably wouldn't get a lot of additional revenue out of that last 5-10% in tax rates. If you were picking the "right" level of taxation, you'd presumably want it to set it somewhere near the point where the economic cost of the taxes was equal to the benefits of the government's use of the revenue, and not at the point of maximum revenue. A 70% marginal rate is not outrageously far from where the top bracket in California will be if Washington decides the best Social Security reform includes lifting the payroll tax cap. Today's effective top marginal rate in CA is ~52% in Fed+State income taxes and another 3.8% for the high-earner Medicare tax. If SS goes uncapped, adding another 12.4%, your $1M earner is hitting 68.2%. I'm dispensing with the accounting fantasy that the "employer-paid" portion of the tax isn't actually a tax on the worker.