Finance
Mortgages, loans, interest and tax. Every result states the method behind it.
Calculators that put a figure on money moving through time — borrowed, earned, or left alone to grow. Each shows its working: the schedule behind an amortisation, the bracket behind a payroll deduction, the compounding period behind an interest figure. Where a number comes from legislation rather than arithmetic, it carries its source and the date it was last checked, because those expire.
Borrowing, earning, or growing
Three groups. Borrowing is the mortgage, loan, car loan, amortisation and credit-card payoff set, all answering what a repayment costs and what the total interest comes to; the amortisation schedule is the one worth opening, because it shows how little of an early payment touches the principal. Earning is salary, paycheck, hours and the time card — gross to net with the deductions itemised. Growing is savings, compound interest, ROI, CAGR, dividends, 401(k) and retirement.
Sales tax lives here because it is a deduction from a personal figure. VAT lives under Business, because it is a trader’s obligation with a reclaim on the other side of it, and confusing the two is a bookkeeping error rather than a rounding one. Invoicing is here for the same logic — it is the document that ends a payment. Fuel costs, tipping and splitting a bill are Everyday: arithmetic about a purchase, not about a balance.