20% is an easy mental calculation, so that's what I do most often these days. I round up to the next dollar or sometimes next multiple of 5 depending on the total amount of the check.

The graph at the bottom of this article may be interesting this context, it's from 2014, but it's all I could find with a quick search: https://www.epi.org/publication/waiting-for-change-tipped-mi...

The tipped minimum wage hasn't changed since 1991. At around 88-89, the difference (in 2014 dollars) between tipped minimum wage and the minimum wage was 40% in 2014 it was 71%.

That depends on the state. For example, all west coast states have the same minimum wage regardless of tipped or non-tipped. See https://en.wikipedia.org/wiki/Tipped_wage

> In the state of Alaska, California, Minnesota, Montana, Nevada, Oregon, Washington, same minimum wage are applied for both tipped and non-tipped employees. Tips collected by employees in these states will not offset employer's obligation to pay the wage, and tips is the additional income beyond the wage paid by employer.