How do you do tax planning?

Question

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.

cutthegrass2 · Accepted Answer

In the UK, HMRC (gov agency that is responsible for collecting tax) has a concept of Payment on Account [1]. You make 2 payments each year (Jan and Jul). The payments are based on last years actual tax liability, so the assumption is you're earning broadly the same as the year pervious. The 2 payments made are then subtracted from your actual liability for the year once calculated.
Perhaps implementing something like the above, just for yourself, would keep you broadly on track to cover your annual tax liability?
[1] https://www.gov.uk/understand-self-assessment-bill/payments-...