cic - compound interest calculator

The cic command calculates compound interest. The results of the calculation are output as either a bar graph (plot.png) or in JSON format. The cic command has a mode for starting as a server.

The cis calculates the total final amount of the investment based on the input values for the principal, monthly contribution, annual interest rate, and the number of years of contribution.

Build

$ cargo build --release

Install

$ cargo install --path .

Usage

$ cic --help
cis - Calculates Compound Interest.
Output the results of compound interest calculations as either a line graph image or JSON.

Usage: cic [OPTIONS] [COMMAND]

Commands:
  server  Starts the server mode
  help    Print this message or the help of the given subcommand(s)

Options:
  -p, --principal <PRINCIPAL>        The principal at the time you started investing. Defaults to 0
  -c, --contribution <CONTRIBUTION>  The monthly contribution amount. Defaults to 1
  -r, --rate <RATE>                  The annual interest rate (in %). Defaults to 5
  -y, --years <YEARS>                The number of years for contributions. Defaults to 5
  -j, --json                         Output as JSON. Defaults to false
  -h, --help                         Print help

Example

Output plot.png

$ cic --principal 1000000 --contribution 100000 --rate 10 --years 10

Output json

$ ./target/debug/cic --principal 1000000 --contribution 100000 --rate 10 --years 5 --json
[
  {
    "year": 1,
    "principal": 1000000.0,
    "annual_contribution": 1200000.0,
    "total_contribution": 1200000.0,
    "annual_interest": 100000.0,
    "total_interest": 100000.0,
    "total_amount": 2300000.0
  },
  {
    "year": 2,
    "principal": 1000000.0,
    "annual_contribution": 1200000.0,
    "total_contribution": 2400000.0,
    "annual_interest": 230000.0,
    "total_interest": 330000.0,
    "total_amount": 3730000.0
  },
  {
    "year": 3,
    "principal": 1000000.0,
    "annual_contribution": 1200000.0,
    "total_contribution": 3600000.0,
    "annual_interest": 373000.0,
    "total_interest": 703000.0,
    "total_amount": 5303000.0
  },
  {
    "year": 4,
    "principal": 1000000.0,
    "annual_contribution": 1200000.0,
    "total_contribution": 4800000.0,
    "annual_interest": 530300.0,
    "total_interest": 1233300.0,
    "total_amount": 7033300.0
  },
  {
    "year": 5,
    "principal": 1000000.0,
    "annual_contribution": 1200000.0,
    "total_contribution": 6000000.0,
    "annual_interest": 703330.0,
    "total_interest": 1936630.0,
    "total_amount": 8936630.0
  }
]

Sever mode

$ cic server
Starting server, port: 8080
POST /compound-interests

$ curl -X POST "http://localhost:8080/compound-interests" \
  -H "Content-Type: application/json" \
  -d '{"principal": 1000000, "contribution": 100000, "rate": 10, "years": 2}' | jq .
[
  {
    "annual_contribution": 1200000.0,
    "annual_interest": 100000.0,
    "principal": 1000000.0,
    "total_amount": 2300000.0,
    "total_contribution": 1200000.0,
    "total_interest": 100000.0,
    "year": 1
  },
  {
    "annual_contribution": 1200000.0,
    "annual_interest": 230000.0,
    "principal": 1000000.0,
    "total_amount": 3730000.0,
    "total_contribution": 2400000.0,
    "total_interest": 330000.0,
    "year": 2
  }
]

License

MIT

Contributing

First off, thanks for taking the time to contribute! ❤️ See CONTRIBUTING.md for more information. Contributions are not only related to development. For example, GitHub Star motivates me to develop!

Side note

The cic command is my first project in Rust. I am using it to learn how to write and structure projects in Rust.

Why did I choose the theme of compound interest?

In Japan, the small amount investment tax exemption system (NISA) started gaining traction in 2024. I was fortunate enough to get involved in a NISA app at work.

This led me to develop an interest in investments. So, it's not surprising that I chose compound interest as my theme.