Guides
Short, practical explanations of the money and math behind our calculators.
How to calculate a monthly loan paymentThe formula, a full worked example, and the spreadsheet shortcut.How compound interest worksWhy interest on interest is so powerful, with clear examples.How to calculate percentage changeThe formula for percent increase and decrease, plus the mistakes to avoid.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.