io.github.VladimirWrites/nestegg-calculators

Interest-only monthly payment on a balance.

Split an option premium into intrinsic value (in-the-money amount) and time value.

Internal rate of return: the per-period rate that zeroes the NPV of a cashflow series. Returns a percent, or null when the series never crosses zero.

Effective APR including upfront fees: the note-rate payment priced against the net proceeds (amount - fees). Annual percent.

Time and interest saved by paying a fixed extra amount every month on a loan, versus the baseline schedule.

Loan-to-value ratio, percent (loan / property value).

Convert between margin and markup. Supply any one of cost/price plus one of marginPct/markupPct (or both cost and price); returns cost, price, profit, marginPct, and markupPct.

Maximum drawdown of a value series: the largest peak-to-trough decline, as a positive percent.

Modified internal rate of return: negatives financed at financeRate, positives reinvested at reinvestRate. Percents in and out.

Maximum loan and home price the income supports: the DTI cap on gross monthly income (less existing debts) sets the payment, whose present value at the rate and term is the loan.

Net worth: assets minus liabilities.

Net operating income: gross rental income less vacancy and operating expenses.

Net present value of a cashflow series (index 0 is today; outflows negative) discounted at a per-period rate.

Break-even underlying price at expiry: strike + premium for a call, strike - premium for a put.

Black-Scholes greeks for a European option: delta, gamma, vega (per 1% vol), theta (per day), rho (per 1% rate).

Simple payback period: periods until cumulative cashflows recover the initial cost, interpolated within the crossing period. Null if never.

Percentage change from one value to another. Null when the starting value is zero.

Present value of a level or growing perpetuity: payment / (rate - growth). Null when growth is not below the rate.

Mortgage points break-even: the upfront cost to buy down the rate, the monthly payment saving, and the whole months to recoup it.

How many years a balance lasts while withdrawing from it: the balance grows each year, then the withdrawal (optionally stepping up) is taken. Returns the depletion year, or sustainable=true when it outlasts 200 years.

Present value of a single future amount discounted annually. The inverse of future-value.

Put-call parity: given one option price, returns both. Provide call or put, plus spot, strike, years, and the rate.

Quick (acid-test) ratio: (current assets - inventory) over current liabilities.

Real (inflation-adjusted) return from a nominal rate via the Fisher relation: (1+nominal)/(1+inflation) - 1.

Refinance break-even: monthly saving, whole months to recoup closing costs, and (if remainingMonths given) the net saving over the remaining term.

Inverse of contributions: the fixed monthly amount needed to reach a target future value over a number of months, given an optional starting balance.

Annual return needed to grow a starting value to a target over a number of years, optionally with a fixed annual contribution. With no contribution this equals CAGR. Returns a percent, or null when unreachable.

Mean, sample variance, and sample standard deviation (n-1) of a series of returns. Pass percents to get a percent stdev (volatility).

Return on assets, percent: net income over total assets.

Return on equity, percent: net income over shareholders' equity.

Return on investment: total percent gain, plus the annualized rate when a holding period in years is given.

Years to double: the rule-of-72 estimate (72/rate) and the exact figure (ln2 / ln(1+rate)).

Hourly rate implied by an annual salary.

Fraction of income saved (savings divided by income). Returns a decimal.

Sharpe ratio: excess mean return per unit of volatility, (mean - riskFree) / stdev. Null when volatility is undefined or zero.

Straight-line depreciation: value falling evenly to a salvage value over a useful life.

Stacked discounts applied in order: the final price and the effective single discount rate.

Sum-of-the-years'-digits depreciation: the depreciable base weighted toward the early years.

Tax-equivalent yield: the taxable yield that matches a tax-free (e.g. muni) yield. Percents in and out.

Progressive tax from caller-supplied brackets. No jurisdiction, year, or rates are baked in: pass the brackets yourself. Returns total tax, effective rate, and marginal rate.

Tip and split: the tip amount, the total, and the per-person share.

Unit price: price divided by quantity (for comparing pack sizes). Null when quantity is zero.

Units-of-production depreciation: the depreciable base spread over total expected units, charged by the units used this period.

Value-added tax (MwSt/USt, sales tax) on a price. By default adds the tax to a net price; with inclusive=true treats the amount as gross and extracts the tax. The rate is always an input (19 or 7 for Germany, etc.).

Weighted average cost of capital: equity and after-tax debt weighted by the capital structure. Percents in and out.

Date-aware internal rate of return: the annual rate that zeroes the XNPV of irregular dated cashflows. Null if no rate fits.

Date-aware net present value: each amount discounted by its fractional years (act/365) from the first cashflow's date. Annual rate in percent.

Bond yield to maturity: the nominal annual yield that prices a bond at the given price, with periodic coupons and face returned at maturity. Solved numerically. Returns a percent, or null.

Price of a zero-coupon bond: face value discounted to today at the yield.