Finance guides
Short, precise explanations of the concepts behind the calculators — how interest really works, what the formulas assume, and how to compare your options.
Every guide here exists to answer a question the calculators raise. If a tool told you that extra payments save $58,000, the matching guide explains the mechanics behind that number; if two loan offers look similar, the comparison guide shows which four figures actually decide it. Each article states its assumptions, works through at least one example with real arithmetic, and links to the calculator where you can test the idea with your own numbers. Start with the guide closest to the decision in front of you — they are written to stand alone.
GuideAPR vs Interest Rate: What's the Difference?What APR includes that the interest rate doesn't, and a computed case where the lower rate loses.GuideDebt Snowball vs Debt AvalancheA computed four-debt case study of both payoff orders, plus when the avalanche edge is big or trivial.GuideHow Compound Interest WorksThe mechanism of interest-on-interest: frequency effects, the Rule of 72 tested, and time asymmetry.GuideHow EMI Is CalculatedThe EMI formula dissected, a ₹25 lakh loan computed by hand, and the flat-vs-reducing rate trap.GuideHow Extra Loan Payments Reduce InterestThe mechanics of prepayment: where the money goes, why timing matters 3x, and when not to prepay.GuideHow Inflation Affects Your SavingsThe arithmetic of purchasing power: real returns, computed examples, and honest options for savers.GuideHow Loan Amortization WorksThe payment formula read in plain words, a schedule built by hand, and the principal crossover located.GuideHow Loan Interest WorksHow interest accrues on a reducing balance, why early payments favor interest, and the flat-rate trap.GuideHow Much Emergency Fund Do You Need?Sizing the fund from essential expenses, a computed funding timeline, and why it shouldn't be invested.GuideHow to Compare Loan OffersA repeatable process for choosing between loans: normalize, compute totals, break-even, fine print.GuideLump Sum vs Monthly InvestingWhat the math says about investing all at once versus averaging in — and when each approach fits.GuideRent vs Buy: What Costs Should You Compare?The complete cost checklist for an honest rent-vs-buy comparison, on both sides of the ledger.