Calculators

A percentage is simply a fraction of 100 — 25% means 25 out of every 100. To find a percentage of a number, convert the percent to a decimal (divide by 100) and multiply: 25% of 80 is 0.25 × 80 = 20. Working backwards, if you know the part and the whole, divide the part by the whole and multiply by 100 to get the percentage — 20 out of 80 is (20 ÷ 80) × 100 = 25%. Percentage change (used for discounts, raises, and growth) is the difference between two values divided by the original value, then multiplied by 100. A price that rises from 40 to 50 has increased by ((50 − 40) ÷ 40) × 100 = 25%. It's easy to confuse percentage change with percentage points — a rate moving from 10% to 15% is a 5 percentage-point increase, but a 50% relative increase. Retailers, payroll departments, and lenders all use these same three calculations — of, change, and reverse — which is exactly what the Percentage Calculator on this page automates, showing the formula alongside the answer so the logic stays visible.

Amortization is the schedule by which a loan is paid off through regular installments that each cover a mix of interest and principal. Early in the loan, most of each payment goes toward interest because the outstanding balance is largest; as the balance shrinks, a growing share of every payment reduces principal instead. This is why two loans with the same monthly payment can leave very different balances after five years if their interest rates differ. The standard formula for a fixed monthly payment uses the loan amount, the monthly interest rate, and the number of payments, and it assumes the rate and payment stay constant for the life of the loan. Extra payments made early — even small ones — cut more from the principal while the interest portion is still high, which is why paying a little more than the minimum in year one saves more total interest than the same extra payment made in year twenty. The Loan Calculator and Mortgage Calculator on FlowUtil apply this formula directly so you can compare payment amounts, total interest paid, and payoff timelines before committing to a loan term.

Body Mass Index (BMI) is a simple screening ratio calculated from height and weight — weight in kilograms divided by height in meters squared. It was designed to flag population-level trends, not to diagnose an individual's health, which is why doctors treat it as one data point rather than a verdict. The commonly used bands are under 18.5 (underweight), 18.5–24.9 (typical range), 25–29.9 (above typical range), and 30+ (well above typical range), though these thresholds were calibrated on average adult body types and don't account for muscle mass, bone density, age, or sex. An athlete with a high muscle-to-fat ratio can register a BMI in the 'above typical' band while carrying very little body fat, and older adults can have a healthy BMI reading while carrying less muscle than is ideal. Because of these limits, BMI is best used as a quick starting point alongside other measures — waist circumference, activity level, and a conversation with a healthcare provider — rather than as a stand-alone health score. The BMI Calculator on this page returns the number and its band instantly from height and weight in either metric or imperial units.