Compound — Compound Interest Calculator

Compound is a command-line compound interest calculator that helps you plan investments, compare interest rates, build amortization schedules, and project financial growth over time.

All calculation history is stored in ~/.compound/data.jsonl as JSONL records for future reference and comparison.

Prerequisites

• Python 3.8+ with standard library
• bash shell

Commands

calculate

Calculate compound interest for a given principal, rate, and time period.

Environment Variables:

• PRINCIPAL (required) — Initial investment amount
• RATE (required) — Annual interest rate as percentage (e.g., 5.5)
• YEARS (required) — Number of years
• FREQUENCY — Compounding frequency: daily, monthly, quarterly, annually (default: monthly)
• CONTRIBUTION — Regular contribution amount (default: 0)
• CONTRIB_FREQ — Contribution frequency: monthly, quarterly, annually (default: monthly)

Example:

PRINCIPAL=10000 RATE=7.5 YEARS=20 FREQUENCY=monthly bash scripts/script.sh calculate

compare

Compare multiple interest rate or compounding frequency scenarios side by side.

Environment Variables:

• PRINCIPAL (required) — Initial investment amount
• RATES (required) — Comma-separated list of rates to compare (e.g., "3,5,7,10")
• YEARS (required) — Number of years
• FREQUENCY — Compounding frequency (default: monthly)

schedule

Generate a detailed payment/growth schedule showing balances at each period.

Environment Variables:

• PRINCIPAL (required) — Initial investment amount
• RATE (required) — Annual interest rate as percentage
• YEARS (required) — Number of years
• FREQUENCY — Compounding frequency (default: monthly)
• CONTRIBUTION — Regular contribution amount (default: 0)

table

Display a year-by-year summary table of investment growth.

Environment Variables:

• PRINCIPAL (required) — Initial investment amount
• RATE (required) — Annual interest rate
• YEARS (required) — Number of years
• CONTRIBUTION — Regular contribution (default: 0)

rate

Calculate the required interest rate to reach a financial goal.

Environment Variables:

• PRINCIPAL (required) — Starting amount
• TARGET (required) — Target amount
• YEARS (required) — Time period in years
• FREQUENCY — Compounding frequency (default: monthly)

goal

Calculate how long it takes to reach a savings goal.

Environment Variables:

• PRINCIPAL (required) — Starting amount
• TARGET (required) — Goal amount
• RATE (required) — Annual interest rate
• CONTRIBUTION — Regular contribution (default: 0)

chart

Generate an ASCII chart of investment growth over time.

Environment Variables:

• PRINCIPAL (required) — Initial amount
• RATE (required) — Annual interest rate
• YEARS (required) — Number of years
• WIDTH — Chart width in characters (default: 60)
• HEIGHT — Chart height in lines (default: 20)

export

Export calculation history to a file.

Environment Variables:

• OUTPUT — Output file path (default: stdout)
• FORMAT — Export format: json, csv, jsonl (default: json)
• CALC_ID — Specific calculation ID to export (default: all)

config

View or update default configuration settings.

Environment Variables:

• KEY — Configuration key to set
• VALUE — Configuration value

history

View past calculations with their results.

Environment Variables:

• LIMIT — Maximum entries to display (default: 20)
• SORT — Sort by: date, principal, rate, total (default: date)

help

Display usage information and available commands.

version

Display the current version of the compound tool.

Data Storage

All calculations are stored in ~/.compound/data.jsonl. Each line is a JSON object with fields:

• id — Unique calculation identifier
• timestamp — ISO 8601 creation time
• type — Calculation type (calculate, compare, goal, etc.)
• params — Input parameters
• result — Calculation results (final amount, interest earned, etc.)

Configuration

Config stored in ~/.compound/config.json:

• default_frequency — Default compounding frequency (default: monthly)
• currency_symbol — Currency symbol for display (default: $)
• decimal_places — Number of decimal places (default: 2)

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