I have been doing some financial planning, and needed to make sure I hadn’t gotten mixed up when trying to keep track of how much money will be where at some point in the future as I shuffle it around between accounts. The spreadsheet I tried to build got unwieldy quickly and I decided I needed a special-purpose tool. I’ve heard of hledger and beancount, and briefly tried them out a few years ago, but they do way more than I needed for this task and I wanted to avoid getting distracted by learning a new tool. So in the end I coded up a special-purpose tool to help, and it seemed interesting enough that I decided to write about it here.