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RiverMath

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Money and investing

VAT, loans, a mortgage, compound growth, FIRE and a cash buffer.

VAT

Add or remove VAT. Handy for 23% in Poland, 19% in Germany, or any rate you set.

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Tip

Tip from a bill and a percent, then split the total between people.

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Split a bill

Split a bill (and an optional tip) so the shares add back to the total.

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Discount

Original price and percent off. See the sale price and what you save.

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Margin and markup

Profit, margin % and markup % from cost and selling price.

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Break-even

How many units cover fixed costs at your price and variable cost.

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Loan overpay

Fixed-rate amortisation. See what an extra monthly payment saves in time and interest.

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Debt payoff

Months to clear a balance at a fixed APR and a fixed payment.

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Mortgage

Monthly payment from price, down payment, rate and term. Equal or declining instalments.

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Rent vs buy

Cash spent on a mortgage plus housing costs versus rent, and a rough equity figure after a chosen number of years.

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Rental yield

Gross and net yearly yield from purchase price, rent, vacancy and running costs.

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Buying power

Move an amount between years with a Polish CPI sketch or with a rate you type.

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Future price

A sum after N years at a constant inflation rate.

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Compound interest

Future value of a starting amount plus optional monthly deposits.

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CAGR

The constant yearly rate that takes a start value to an end value.

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ROI

Gain over cost, and an annualised rate if you enter the years.

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Simple payback

Years until a yearly saving covers what you spent.

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Savings goal

How long a monthly deposit takes to reach a target, with optional interest.

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Savings rate

What share of monthly income you put aside, and the yearly pot.

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Emergency fund

A cash target from monthly spend × months, the gap, and how long the deposit takes.

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FIRE number

A nest egg from yearly spend and a withdrawal rate, then years of saving at a constant return.

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Dividend yield

Yield and yearly cash from a per-share dividend and how many shares you hold.

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Subscriptions

Popular subscriptions with current prices, custom lines and monthly and yearly totals.

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Child cost

A rough lifetime bill from what you spend in a month and how many years you count.

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Statutory interest

Simple interest from the NBP reference rate: ordinary, late-payment, or late payment in commercial deals.

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Rule of 72

Years for a lump to double at a constant yearly rate.

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Real return

A nominal yearly return stripped of inflation.

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NPV

Net present value of a constant yearly payment minus the outlay.

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Annuity payment

The monthly payment that empties a pot over the years at a fixed rate.

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Effective APR

The yearly rate after compounding n times.

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