Ask HN: How do you do tax planning?

About a year ago I started putting tax money into a tax account throughout the year, to avoid any surprises come tax season. This has greatly reduced my stress level when I needed to prepare and pay tax. I'd like to continue doing that.

However, one problem is I need to figure out what my tax liability is, and how much I've paid/reserved, up to the current date of the tax year. Since I do my own accounting, all I'm missing right now is plugging in the numbers into form 1040, and get a number out. Ideally I can automate this process so I don't have to fill the form twice every month. I can probably write a program or create a spreadsheet, but I'm wondering if there's an existing solution already.