This looks really cool I've used beancount/fava for tax planning, but of course I had to code up my own tax models. In the US tax table change every year (by a predictable formula) and some forms of income are weird, like I bonds are exempt from federal tax, but are taxed by state income tax. It seems unlikely that you could support all the cases, but is there a straightforward way to plug in your own model? I did see in tax.go you had long term, short term, but couldn't quite find the income tax tables, like long term capital gains has different rates depending upon filing status and amount.