io.github.VladimirWrites/nestegg-calculators

Accrued interest since the last coupon: the annual coupon pro-rated by days elapsed over the day-count basis.

After-tax yield: a yield reduced by the tax rate. Percents in and out.

Monthly loan amortization schedule and summary. Supports dated extra principal payments and a rate-fixed period. detail controls output size: 'summary' (default) returns totals plus a per-year breakdown; 'monthly' returns the full schedule (paginate with offset/limit). Returns numbers and schedules; no advice.

Future value of an ordinary annuity. rate is the per-period rate in percent.

The level payment that amortizes a present value over n periods (the loan-payment formula). rate is per period.

Present value of an ordinary annuity (level payment at each period end). rate is the per-period rate in percent.

Balloon loan: payment based on a long amortization, with the balloon being the balance still due after the shorter balloon term.

Barista FIRE: the nest egg needed when part-time income covers part of the spending, so the portfolio only funds the remainder at the safe withdrawal rate.

Biweekly mortgage acceleration: paying half the monthly payment every two weeks. Returns the biweekly payment and the months and interest saved.

Black-Scholes price of a European call or put option, plus d1/d2. Volatility and rates in percent; optional continuous dividend yield.

Macaulay duration (PV-weighted average time of cashflows, in years) and modified duration (price sensitivity to yield).

Price of a coupon bond given a yield: present value of the coupons plus the face at maturity.

Break-even volume: fixed costs divided by the per-unit contribution (price - variable cost), plus the revenue at that volume.

The 50/30/20 budget split of monthly income into needs, wants, and savings.

Compound annual growth rate between two values over a number of years. Returns a decimal (0.07 means 7%).

Capitalization rate: net operating income as a percent of property value.

Cash-on-cash return: annual pre-tax cash flow as a percent of the cash invested.

Coast FIRE: whether the current nest egg, left to grow untouched to retirement, already reaches the FIRE target. Returns the target, the projected balance, whether it coasts, and any shortfall.

Compound growth at any frequency, with an optional contribution each period (paid at period end). Generalizes future-value (periodsPerYear 1) and contributions (periodsPerYear 12).

Contribution margin per unit and as a percent of price.

Future value of a fixed monthly contribution, optionally stepping up each year.

Bond convexity (years^2): the curvature of price with respect to yield, used alongside duration.

Months to clear a credit-card balance at a fixed monthly payment, plus interest paid. Null when the payment can't cover the first month's interest.

Current ratio: current assets over current liabilities.

Current yield: the annual coupon as a percent of the bond's current price.

German flat tax on capital income (Abgeltungsteuer, §32d EStG) for tax years 2023-2026 with the year's Sparerpauschbetrag built in. 25% above the allowance, Soli 5.5% on top (no Freigrenze for capital income), and with church tax the statutory reduced rate (e.g. 24.45% at 9%) plus the church tax itself.

German net (Netto) salary from gross (Brutto). No tax tables are baked in: look up the current year's statutory figures and pass them in. Income tax (Lohnsteuer) and Soli are amounts; church tax is a percent of the income tax; the four employee social rates and the two contribution ceilings are inputs. Use consistent units (e.g. all annual).

German child benefit (Kindergeld) for 2023-2026: the year's flat monthly amount per child (uniform since 2023), as monthly and annual totals.

German Midijob / Uebergangsbereich (paragraph 20 Abs. 2a SGB IV) for 2023-2026: classifies a monthly pay as Minijob / Midijob / regular against the year's thresholds and, inside the Midijob band, computes the reduced contribution bases (Faktor F from the year's rates) and the employee vs employer social-insurance split.

Exact German net (Netto) salary from annual gross (Brutto) for tax years 2023-2026. Income tax and Soli follow the official BMF Programmablaufplan for the year (to the euro; 2024 uses the retroactive December tariff), church tax comes from the PAP's Kirchensteuer base, and employee social insurance uses that year's ceilings and rates (KV Zusatzbeitrag defaults to the year's average). Earlier years are rejected - use de-gross-to-net with self-supplied figures instead.

German pension points (Entgeltpunkte, paragraph 63 SGB VI) for 2023-2026: points earned from an annual gross via the year's Durchschnittsentgelt (capped at the contribution ceiling), the aktueller Rentenwert for both halves of the year, and optionally the gross monthly state pension for a total point count.

Multi-debt payoff plan under a fixed monthly budget. method 'avalanche' (highest rate first) minimizes interest; 'snowball' (smallest balance first) clears accounts soonest. Returns months, total interest, and payoff order; flags insolvent budgets.

Declining-balance depreciation: a fixed percent of the reducing book value, for a given year. Returns that year's depreciation and the remaining book value.

Value after compounding down (or up) at a yearly percentage rate over a number of years. This is the method the app uses for long-term assets.

A single percentage discount: the amount off and the final price.

Discounted payback period: like payback-period but each cashflow is discounted at the per-period rate.

Dollar-cost averaging: buying a fixed amount each period at the given prices. Returns units accumulated, total invested, average cost, and final value at the last price.

Double-declining-balance depreciation: 2/usefulYears of the book value each year, not falling below salvage.

Debt service coverage ratio: net operating income divided by annual debt service.

Debt-to-income ratio, percent (monthly debt / gross monthly income).

Convert a nominal annual rate to the effective annual rate (APY) for a compounding frequency, or with toNominal recover the nominal rate from an APY.

Months of runway: liquid savings divided by monthly expenses.

Effect of an annual fee: the compounded balance at the gross rate vs net of the fee, and the amount lost to fees.

FIRE target nest egg from annual spend and a safe withdrawal rate (default 4%), plus the gap from today and the years to reach it given optional savings and growth. No advice.

Future value of a single lump sum compounded annually.

Convert an amount using a rate supplied by the caller (units of target currency per unit of source). No rate is ever looked up.

Gross rent multiplier: price divided by gross annual rent.

Holding-period return: (income + capital gain) / starting value, in percent.

Annualize an hourly rate (and the monthly equivalent).

Convert a nominal amount to today's purchasing power (real), or with toNominal inflate a real amount forward, at a given annual inflation rate.

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.