finance

March 28, 2026 · View on GitHub

A collection of financial calculators for everyday money math.

Usage

openGyver finance [subcommand] [flags]

Global Flags (inherited by all subcommands)

Flag	Short	Type	Default	Description
`--json`	`-j`	bool	`false`	Output results as machine-readable JSON
`--help`	`-h`	bool		Show help for the command

Subcommands

loan

Calculate monthly payment, total payment, and total interest for a fixed-rate loan or mortgage.

Uses the standard amortisation formula:

M = P * [r(1+r)^n] / [(1+r)^n - 1]

where P = principal, r = monthly interest rate, n = total number of monthly payments.

Arguments

Argument	Required	Description
(none)		All input is provided via flags

Flags

Flag	Type	Description
`--principal`	float	Loan amount in dollars (required)
`--rate`	float	Annual interest rate as a percentage (required)
`--years`	int	Loan term in years (required)

Examples

# 30-year mortgage at 6.5%
openGyver finance loan --principal 250000 --rate 6.5 --years 30

# 5-year car loan at 4.9%
openGyver finance loan --principal 35000 --rate 4.9 --years 5

# 15-year mortgage at 5.75% (JSON output)
openGyver finance loan --principal 400000 --rate 5.75 --years 15 -j

# Student loan
openGyver finance loan --principal 50000 --rate 5.0 --years 10

# Small personal loan
openGyver finance loan --principal 10000 --rate 8.5 --years 3

# Compare 15-year vs 30-year mortgage
openGyver finance loan --principal 300000 --rate 6.0 --years 15
openGyver finance loan --principal 300000 --rate 6.5 --years 30

# JSON output piped to jq
openGyver finance loan --principal 200000 --rate 7 --years 30 -j | jq '.monthly_payment'

JSON Output Format

{
  "principal": 250000,
  "annual_rate": 6.5,
  "years": 30,
  "monthly_payment": 1580.17,
  "total_payment": 568861.22,
  "total_interest": 318861.22
}

compound

Calculate the future value of an investment with compound interest.

Uses the compound interest formula:

A = P * (1 + r/n)^(n*t)

where P = principal, r = annual rate, n = compounding frequency per year, t = time in years.

Common compounding frequencies:

Value	Meaning
1	Annually
4	Quarterly
12	Monthly (default)
52	Weekly
365	Daily

Arguments

Argument	Required	Description
(none)		All input is provided via flags

Flags

Flag	Type	Default	Description
`--principal`	float		Initial investment amount (required)
`--rate`	float		Annual interest rate as a percentage (required)
`--years`	int		Investment period in years (required)
`--frequency`	int	`12`	Compounding frequency per year

Examples

# \$10,000 at 7% for 10 years, compounded monthly
openGyver finance compound --principal 10000 --rate 7 --years 10

# \$5,000 at 5% for 20 years, compounded daily
openGyver finance compound --principal 5000 --rate 5 --years 20 --frequency 365

# \$25,000 at 8.5% for 5 years, compounded quarterly
openGyver finance compound --principal 25000 --rate 8.5 --years 5 --frequency 4

# Retirement savings: \$100k at 7% for 30 years
openGyver finance compound --principal 100000 --rate 7 --years 30

# Annual compounding
openGyver finance compound --principal 10000 --rate 5 --years 10 --frequency 1

# JSON output
openGyver finance compound --principal 50000 --rate 6 --years 15 -j

# Weekly compounding
openGyver finance compound --principal 10000 --rate 4.5 --years 5 --frequency 52

# Compare daily vs monthly compounding
openGyver finance compound --principal 10000 --rate 5 --years 10 --frequency 12
openGyver finance compound --principal 10000 --rate 5 --years 10 --frequency 365

JSON Output Format

{
  "principal": 10000,
  "annual_rate": 7,
  "years": 10,
  "frequency": 12,
  "final_amount": 20096.61,
  "total_interest": 10096.61
}

roi

Calculate the return on investment (ROI) given an initial investment and a final value.

ROI = ((final - initial) / initial) * 100

Positive ROI indicates a profit; negative ROI indicates a loss.

Arguments

Argument	Required	Description
(none)		All input is provided via flags

Flags

Flag	Short	Type	Default	Description
`--initial`		float		Initial investment amount (required)
`--final`		float		Final value of the investment (required)

Examples

# Bought at \$1,000, now worth \$1,500 (50% ROI)
openGyver finance roi --initial 1000 --final 1500

# Bought at \$5,000, sold for \$3,750 (a loss)
openGyver finance roi --initial 5000 --final 3750

# JSON output
openGyver finance roi --initial 200 --final 350 -j

# Real estate investment
openGyver finance roi --initial 250000 --final 375000

# Stock investment loss
openGyver finance roi --initial 10000 --final 8500

# Doubled your money
openGyver finance roi --initial 5000 --final 10000

# Pipe JSON to jq
openGyver finance roi --initial 1000 --final 1250 -j | jq '.roi_percent'

# Break even
openGyver finance roi --initial 1000 --final 1000

JSON Output Format

{
  "initial": 1000,
  "final": 1500,
  "profit_loss": 500,
  "roi_percent": 50
}

tip

Calculate tip, total bill, and per-person share when splitting the bill among multiple people.

Arguments

Argument	Required	Description
(none)		All input is provided via flags

Flags

Flag	Type	Default	Description
`--amount`	float		Bill amount before tip (required)
`--percent`	float	`18`	Tip percentage
`--split`	int	`1`	Number of people splitting the bill

Examples

# Standard 18% tip on \$85.50
openGyver finance tip --amount 85.50

# 20% tip on \$120, split 4 ways
openGyver finance tip --amount 120 --percent 20 --split 4

# 15% tip on \$45.00
openGyver finance tip --amount 45 --percent 15

# Generous 25% tip
openGyver finance tip --amount 200 --percent 25

# Split between 6 people
openGyver finance tip --amount 350 --percent 20 --split 6

# JSON output
openGyver finance tip --amount 85.50 --percent 20 -j

# Minimal tip
openGyver finance tip --amount 30 --percent 10

# Large party dinner split
openGyver finance tip --amount 800 --percent 18 --split 10

JSON Output Format

{
  "amount": 85.5,
  "percent": 20,
  "tip": 17.1,
  "total": 102.6,
  "split": 4,
  "per_person": 25.65
}

tax

Calculate the tax amount and total price given a pre-tax amount and a tax rate.

Arguments

Argument	Required	Description
(none)		All input is provided via flags

Flags

Flag	Short	Type	Default	Description
`--amount`		float		Pre-tax amount (required)
`--rate`		float		Tax rate as a percentage (required)

Examples

# 8.25% sales tax on \$99.99
openGyver finance tax --amount 99.99 --rate 8.25

# 10% tax on \$250
openGyver finance tax --amount 250 --rate 10

# JSON output
openGyver finance tax --amount 49.95 --rate 7.5 -j

# High tax rate
openGyver finance tax --amount 500 --rate 20

# Vehicle purchase tax
openGyver finance tax --amount 35000 --rate 6.5

# Low tax rate
openGyver finance tax --amount 15.99 --rate 4

# Pipe JSON to jq
openGyver finance tax --amount 100 --rate 8.875 -j | jq '.total'

# Multiple items total
openGyver finance tax --amount 1234.56 --rate 9.5

JSON Output Format

{
  "amount": 99.99,
  "rate": 8.25,
  "tax": 8.25,
  "total": 108.24
}

salary

Convert salary or wages between different pay periods.

Assumes a standard full-time work schedule:

8 hours per day
5 days per week
4.33 weeks per month (52/12)
52 weeks per year

Valid period values: hourly, daily, weekly, monthly, yearly

The text output shows all pay period conversions at once, regardless of the --to flag.

Arguments

Argument	Required	Description
(none)		All input is provided via flags

Flags

Flag	Type	Description
`--amount`	float	Salary/wage amount (required)
`--from`	string	Source pay period: hourly, daily, weekly, monthly, yearly (required)
`--to`	string	Target pay period: hourly, daily, weekly, monthly, yearly (required)

Examples

# Hourly to yearly
openGyver finance salary --amount 50 --from hourly --to yearly

# Yearly to hourly
openGyver finance salary --amount 100000 --from yearly --to hourly

# Monthly to weekly
openGyver finance salary --amount 8000 --from monthly --to weekly

# Daily to monthly
openGyver finance salary --amount 400 --from daily --to monthly

# JSON output
openGyver finance salary --amount 75 --from hourly --to yearly -j

# Weekly to yearly
openGyver finance salary --amount 2000 --from weekly --to yearly

# Compare hourly rates
openGyver finance salary --amount 120000 --from yearly --to hourly

# Monthly to daily
openGyver finance salary --amount 6500 --from monthly --to daily

JSON Output Format

{
  "amount": 50,
  "from": "hourly",
  "to": "yearly",
  "result": 104000
}

discount

Calculate the discount amount and final price after applying a percentage discount.

Arguments

Argument	Required	Description
(none)		All input is provided via flags

Flags

Flag	Short	Type	Default	Description
`--price`		float		Original price (required)
`--percent`		float		Discount percentage (required, 0-100)

Examples

# 25% off \$199.99
openGyver finance discount --price 199.99 --percent 25

# 50% off \$80
openGyver finance discount --price 80 --percent 50

# 10% off \$1,250 (JSON output)
openGyver finance discount --price 1250 --percent 10 -j

# Black Friday sale: 40% off
openGyver finance discount --price 599.99 --percent 40

# Small discount
openGyver finance discount --price 29.99 --percent 5

# Full price (0% discount)
openGyver finance discount --price 100 --percent 0

# Pipe JSON to jq for final price only
openGyver finance discount --price 200 --percent 30 -j | jq '.final_price'

# Compare discounts
openGyver finance discount --price 500 --percent 15
openGyver finance discount --price 500 --percent 25

JSON Output Format

{
  "original_price": 199.99,
  "discount_percent": 25,
  "discount_amount": 50,
  "final_price": 149.99
}

margin

Calculate profit, profit margin percentage, and markup percentage given cost and revenue (selling price).

Profit   = Revenue - Cost
Margin % = (Profit / Revenue) * 100
Markup % = (Profit / Cost) * 100

Arguments

Argument	Required	Description
(none)		All input is provided via flags

Flags

Flag	Short	Type	Default	Description
`--cost`		float		Cost of goods/services (required)
`--revenue`		float		Selling price / revenue (required)

Examples

# Cost \$40, selling for \$100
openGyver finance margin --cost 40 --revenue 100

# Cost \$15.50, selling for \$29.99
openGyver finance margin --cost 15.50 --revenue 29.99

# JSON output
openGyver finance margin --cost 250 --revenue 400 -j

# High margin product
openGyver finance margin --cost 5 --revenue 49.99

# Low margin product
openGyver finance margin --cost 80 --revenue 90

# Selling at a loss
openGyver finance margin --cost 100 --revenue 75

# Pipe to jq for margin percent only
openGyver finance margin --cost 30 --revenue 60 -j | jq '.margin_percent'

# Wholesale vs retail
openGyver finance margin --cost 12 --revenue 24.99

JSON Output Format

{
  "cost": 40,
  "revenue": 100,
  "profit": 60,
  "margin_percent": 60,
  "markup_percent": 150
}