Learn the Math
Step-by-step guides explaining the formulas, worked examples, and real-world applications behind every calculator.
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How to Calculate BMI: Formula, Charts, and What It Means
Learn the exact BMI formula, how to calculate it by hand for both metric and imperial units, understand the weight categories, and discover the limitations of BMI as a health metric.
Compound Interest Explained: The Formula, Examples, and Why It Matters
Understand compound interest from first principles. Learn the formula, see worked examples with different compounding frequencies, and discover how small rate differences create massive wealth differences over time.
The Pythagorean Theorem: Proof, Formula, and Real-World Uses
A complete guide to the Pythagorean theorem — from its geometric proof to practical applications in construction, navigation, and everyday life. Includes worked examples and common Pythagorean triples.
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How to Use a Mortgage Calculator: Monthly Payments, Total Cost & Amortization
Step-by-step guide to understanding mortgage calculations. Learn what affects your monthly payment, how to read an amortization schedule, and strategies to pay off your mortgage faster.
How to Calculate Percentage: Every Type, Every Formula
Master all types of percentage calculations — finding a percentage of a number, percentage increase/decrease, reverse percentage, and more. With formulas, worked examples, and mental shortcuts.
How to Calculate GPA: Formula, Letter Grades & Weighted GPA
Complete guide to calculating GPA — unweighted and weighted. Includes the formula, grade point scale, worked examples with credit hours, and how one grade affects your cumulative GPA.
Standard Deviation Explained: Formula, Examples & When to Use It
Understand standard deviation from first principles. Includes the population and sample formulas, a full step-by-step worked example, the 68-95-99.7 rule, z-scores, and real-world applications.
Celsius to Fahrenheit (and Back): Formula, Chart & Quick Tips
The exact Celsius to Fahrenheit formula with worked examples, a full reference chart of common temperatures, mental shortcuts for quick conversion, cooking temperatures, and the history of both scales.
How to Calculate Compound Interest by Hand
Step-by-step walkthrough of the compound interest formula — annual and monthly compounding, the year-by-year method, the Rule of 72, and how to verify your answer against simple interest.
APR vs Interest Rate: What's the Difference and Why It Matters
Learn the real difference between APR and interest rate, what fees go into APR, how to calculate it, and when APR can mislead you — with a worked mortgage example and credit card breakdown.
How to Calculate Area: Formulas for Every Shape
Complete area formula guide covering rectangle, square, triangle, circle, trapezoid, parallelogram, ellipse, sector, annulus, and composite shapes — with worked examples and the reasoning behind each formula.
Fraction to Decimal Conversion: Methods, Charts & Common Values
How to convert any fraction to a decimal using long division or the power-of-10 method. Includes a full reference chart, recurring vs terminating decimals explained, and converting decimals back to fractions.