Guides
Short, practical explanations of the money and math behind our calculators.
Monthly payment formula: how to calculate a loan installmentThe formula, what each letter means, and a worked installment example.How compound interest worksWhy interest on interest is so powerful, with clear examples.Percent change formula: how to calculate percentage increase or decreaseThe formula, worked examples for increase, decrease and year-over-year, and common mistakes.How much house can I afford? The 28/36 ruleA simple income-based method for setting a home budget.How to pay off credit card debt fasterAvalanche versus snowball, with real numbers and a step-by-step plan.How much car can I afford? The 20/4/10 ruleA simple rule for keeping car costs in proportion to your income.The 4% rule: how much do you need to retire?What the 4% rule says, how to use it, and its limits.The 50/30/20 budget rule explainedA simple way to split your income between needs, wants and savings.Profit margin vs markup: what's the difference?Why margin and markup differ, and how to price for the profit you want.BMR and TDEE explainedWhat BMR and TDEE mean and how to use your calorie estimate sensibly.APR vs APY: what's the difference?Why APY is higher than APR, and which one to compare.How loan amortization worksHow each payment splits into interest and principal, and what extra payments do.Should I refinance my mortgage?The break-even test, the term trap and a checklist before you switch.