Guides & tutorials
Short, practical explainers for the numbers in daily life — each one links to the free calculators that put the theory into practice.
How to Calculate Hours Worked
Convert times to 24-hour format, subtract, handle breaks and overnight shifts — with the decimal table payroll uses.
Read guideHow to Calculate Standard Deviation
The standard deviation formula worked through step by step — sample vs population, variance, and how to read the result.
Read guideHow to Calculate Average
How to calculate the mean, when to prefer the median, and what the mode tells you — with worked examples.
Read guideHow to Calculate Mortgage Payments
The amortization formula behind your monthly mortgage payment, with a full worked example and term-length comparison.
Read guideHow to Calculate Sales Tax
Compute sales tax forward from a price, or reverse it out of a receipt total, with the formula and worked examples.
Read guideHow to Calculate GPA
The weighted GPA formula with a worked example: convert letter grades to points, weight by credit hours, and divide.
Read guideHow to Calculate Percentage Increase
The percent change formula with worked examples for increases and decreases, plus the percentage-points trap that catches everyone.
Read guideHow to Calculate Percentage
The percentage formula explained step by step, with shortcuts and worked examples for discounts, scores and everyday percent questions.
Read guideHow to Calculate BMI
How BMI is calculated, what the weight ranges mean, and where the number falls short.
Read guideHow Compound Interest Works
The compound interest formula explained with real numbers, plus three rules of thumb for savings and debt.
Read guideDaily Calories and Macros: A Practical Guide
Estimate your BMR and TDEE, adjust for fat loss or muscle gain, and split calories into protein, carbs and fat.
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