My name is Steve Si (developer of Easy2Boot USB boot software). I am now retired after a lifetime of designing, building and testing computer electronics, writing software (assembler, C, Basic, VBasic, etc.) and eBooks. Like many people, I have started a few investment accounts over the years including a Trading 212 account (my blog is here).
A good capital gains calculator is necessary if you buy and sell shares in a GIA (General Investment Account) because you cannot simply use the figures provided by your broker’s annual report. You must combine all your trades from all your brokers and then apply HMRC share matching rules to work out the taxable gain/loss for each tax year.
The main CG calculator on my home page was written to allow me to simply load all my downloaded broker share transaction .csv files at once. I wanted it to give the same results as the well-used and trusted cgtcalculator.com and also show the workings. As cgtcalculator.com did not provide a conversion tool for Trading 212, I wrote one (which cgtcalculator.com now links to on my blog), but it occurred to me to make a website that would simply process all my shares transaction files.
I then added a few more calculator pages just for fun. The Dividend and Interest page will extract dividend and interest payments from some broker .csv files while the ERI Lookup page attempts to find the ERI notional dividend payments for UK reporting offshore funds that are in your portfolio. These are just tools to help because most brokers do not report ERI at all. For distributed Dividends and Interest on cash however, you should use the figures in each of your brokers annual tax reports. Note that most ETF dividends will be classed as Foreign dividends not UK dividends.
Note: 99% of the app scripts used on this site were written using ChatGPT 5 and Codex as I am not very familiar with Javascript, Python or PHP. Your trade data does not leave your computer. The scripts used are not hidden and are easily viewable, there is no back-server.
Please use the Forum if you have any questions or comments, or you can contact me directly at easy2boot @ gmail dot com.