Guides
Learn how the numbers work
Plain-language explainers behind the calculators — the formulas, the trade-offs, and how to read the results.
How EMI Is CalculatedEMI (equated monthly installment) is calculated from three inputs — the loan principal, the monthly interest rate, and the number of monthly payments — using a fixed formula that produces the same payment amount for every month of the loan.Fixed vs. Variable Rate Mortgages: Which Should You Choose?A fixed-rate mortgage locks in the same interest rate for the entire loan term, so the payment never changes; a variable (or adjustable) rate mortgage starts lower but can rise or fall over time as it tracks a benchmark rate, changing the payment along with it.How Compound Interest WorksCompound interest is interest calculated on both the original principal and on interest already earned in previous periods, so a balance grows faster over time than it would under simple interest, which is calculated on the principal alone.APR vs. Interest Rate: What's the Difference?The interest rate is the cost of borrowing the principal itself, expressed as a yearly percentage; the APR (annual percentage rate) folds in most lender fees and charges on top of that interest, giving a fuller — and usually higher — picture of a loan's true yearly cost.BMI Explained: What It Measures and Where It Falls ShortBMI (body mass index) is a simple screening number calculated from height and weight, used to place adults into broad categories such as underweight, normal weight, overweight, and obese — but it does not directly measure body fat, muscle mass, or overall health.How Percentage Calculations WorkMost everyday percentage problems reduce to one of four formulas: finding p% of a value, finding what percent one value is of another, finding the original value from a percentage, or finding the percent change between two values — each rearranges the same relationship, value = percent × base, around a different unknown.How Unit Conversion WorksUnit conversion works by expressing every unit as a multiple of one shared base unit, then multiplying the starting value by the ratio of the source unit's factor to the target unit's factor — the units themselves cancel out, leaving only the converted number.How to Calculate Age and Date Differences AccuratelyAccurately calculating age or the gap between two dates means comparing full calendar dates — year, month, and day together — rather than just subtracting years, because a birthday that hasn't happened yet in the current year changes the answer by exactly one year.Gross Pay vs. Net Pay: How Salary and Hourly-Rate Calculators WorkSalary calculators convert pay between frequencies — hourly, daily, weekly, monthly, and annual — by anchoring every figure to a shared annual amount; that annual figure is 'gross pay,' before taxes and deductions, which is different from the smaller 'net pay' actually received.