Learn the maths behind every calculator
Long-form explainers on BMI, mortgages, compound interest, percentages, calories, and unit conversions. Written to help you get the right answer, not just a number.
How to Calculate Your Daily Water Intake
How much water do you actually need? A weight-based formula, activity adjustments, climate factors, and signs of dehydration explained with real examples.
How to Calculate Electricity Costs for Home Appliances
The kWh formula explained with real examples for common appliances — AC, fridge, TV, washer — plus five tips to cut your electricity bill immediately.
Mental Math Tricks for Everyday Calculations
Ten mental math techniques for tips, discounts, multiplication, division, and quick estimation — with worked examples and practice tips.
How to Read and Understand Your Credit Score
Credit score ranges explained — from 300 to 850, the five factors that determine your score, and practical steps to improve it in 3–6 months.
How to Calculate GPA: Weighted vs Unweighted Explained
Understand the difference between weighted and unweighted GPA, learn the quality-points formula, and calculate your own GPA step by step.
How to Calculate Your Net Worth
Your net worth = assets minus liabilities. Learn what to include, median benchmarks by age, and the three levers that grow it fastest over time.
How to Calculate Square Footage for Any Room or Space
Measure and calculate the area of any room or space — rectangles, triangles, circles, and irregular shapes — with simple formulas and examples.
Cooking Measurement Conversions: Cups, Tablespoons, Grams, and More
Convert cups, tablespoons, teaspoons, ounces, grams, and millilitres for any recipe. Includes a quick-reference table and baking-specific weight conversions.
How to Calculate the Days Between Two Dates
Step-by-step methods for counting days between dates — leap year handling, business days vs. calendar days, and practical use cases from projects to pregnancy.
How to Calculate a Discount: Percent Off and Sale Price
Master discount calculations — single discounts, stacked discounts, and the real math behind "additional percent off" sales events.
How to Estimate Your Ideal Body Weight
Four widely-used ideal body weight formulas compared — Devine, Robinson, Miller, and Hamwi — with examples, strengths, limitations, and practical context.
How Much Do I Need to Retire? A Simple Calculator Guide
Project your retirement nest egg using compound interest, the 4% rule, and inflation-adjusted returns. Includes a full worked example.
How to Calculate a Restaurant Tip (and When to Tip More)
The simple formulas for calculating tips at restaurants, bars, and takeout. Learn when 15% is enough and when you should tip 20% or more.
How to Calculate Loan Interest: Simple vs. Compound
Simple interest vs. compound interest — the exact formulas, real-number examples for auto and personal loans, and strategies to minimise total interest paid.
How to Pay Off Debt Faster: Snowball vs Avalanche Method
Compare the snowball and avalanche debt payoff strategies side by side. Learn which saves more interest and which keeps you motivated.
Understanding Currency Exchange Rates for Travellers
How exchange rates work, where travellers get the best rates, hidden fees at airports and banks, and quick mental conversion tricks for any currency.
Speed, Distance, and Time: The Formula Everyone Should Know
Master the speed = distance / time formula with real-world examples. Convert between mph, km/h, and m/s for road trips, running, and science.
How to Add, Subtract, Multiply, and Divide Fractions
Step-by-step rules for every fraction operation — common denominators, cross-multiplication, reciprocals — with worked examples and simplification tips.
How to Add and Subtract Fractions (Step-by-Step)
Master fraction arithmetic with clear step-by-step instructions. Covers common denominators, mixed numbers, and how to simplify results.
Speed, Distance, and Time Formula Explained
The speed-distance-time triangle explained — three versions of one formula, worked examples for everyday and physics problems, and common unit pitfalls.
How to Plan for Retirement on a Middle-Class Income
A step-by-step retirement plan for middle-income earners — savings benchmarks, the 4% rule, employer match strategies, and when to start if you are behind.
How to Use the Discount Formula for Shopping Deals
The discount formula explained for every deal type — percentage off, stacked coupons, BOGO, and rebates — with mental math shortcuts and worked examples.
How to Split a Bill and Tip Fairly
Three methods for splitting a restaurant bill — equal, proportional, and item-by-item — with tip formulas, worked examples, and fairness tips for groups.
How Compound Interest Works in a Savings Account
How your savings account compounds interest daily or monthly, the APY vs. APR distinction, and why a 0.5% rate difference matters more than you think over time.
How to Calculate Square Footage for Flooring, Paint, and Tiling
Measure any room accurately for flooring, paint, or tile. Covers rectangular and odd-shaped rooms, waste allowances, and the mistakes that lead to overbuying.
Understanding Amortisation: Where Your Mortgage Payment Goes
How amortisation splits each mortgage payment into principal and interest, why the ratio shifts over time, and how even small extra payments save thousands.
How GPA Is Calculated: High School and College
The complete guide to GPA calculation on a 4.0 scale — unweighted, weighted, credit-hour adjusted — with worked examples for both high school and college.
How to Calculate Sales Tax in Any US State
The exact sales tax formula, how state and local rates stack, which items are exempt, and how to reverse-calculate a pre-tax price — with worked examples.
How to Convert Between Fahrenheit and Celsius Quickly
The exact formulas for Fahrenheit-Celsius conversion, three mental shortcuts that work in seconds, and a quick-reference table for everyday temperatures.
How to Calculate Your Exact Age in Days, Weeks, and Months
Convert your age into days, weeks, and months with the exact formula, leap year handling, and fun milestone numbers you can share.
How to Calculate Calories Burned Walking or Running
The MET formula explained with real examples for walking and running at different speeds — plus why most fitness trackers overestimate your burn.
How to Budget Using the 50/30/20 Rule
The 50/30/20 rule splits your after-tax income into needs, wants, and savings. Learn how to apply it, adapt it, and avoid the most common budgeting mistakes.
How to Calculate Your Debt-to-Income Ratio for a Mortgage
The DTI formula lenders actually use, what counts as debt, the 28/36 rule explained, and five practical ways to improve your ratio before you apply.
Unit Conversion Basics: Metric vs Imperial
A practical walkthrough of converting length, weight, temperature, volume, area, and speed — with the exact factors you actually need and a handful of mental shortcuts.
How to Calculate Calories and Macros for Weight Loss
BMR, TDEE, calorie deficits, and protein/carb/fat splits explained with real numbers — plus the three most common mistakes that stall fat loss.
Percentage Calculations Made Simple
Every percentage problem solved by one of three formulas. Learn them once, add a couple of mental-math shortcuts, and you will never be stumped by a discount tag again.
Mortgage Calculator Explained: Principal, Interest, Taxes & Insurance
Every part of a monthly mortgage payment — PITI, PMI, HOA, and the amortisation schedule — decoded with real numbers and a step-by-step worked example.
Understanding Compound Interest: A Complete Guide
The compound interest formula demystified — with clear examples showing how starting early, compounding frequency, and regular contributions change outcomes.
How to Calculate Your BMI Accurately (With Worked Examples)
The full BMI formula explained, worked examples in both metric and imperial units, the official healthy ranges, and what BMI actually misses.
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