I created a small web application using React.js to calculate interest rates for various investments and evaluate different ETF/fund investment plans and more.

How do I consider inflation? - According to the fisher equation the nominal interest rate can be approximated by subtracting the inflation rate from the (real) interest rate. Therefore I didn’t add an extra input field to the calculator.

What about transaction fees? - Just use net deposit rates. Unfortunately there are so many different pricing models that brokers are using and I didn’t want to make the calculator too complicated by generalising them all.

Financial transaction tax must also be considered (at least in Germany). I didn’t feel the need to include it in the calculator because the tax can simply be subtracted at the end.

Where can I find the source code? - You can find it here on Gitlab. It’s available under the MIT license, so feel free to copy, modify or distribute it.