Calculation Guides
Ten in-depth, plain-English guides on the maths behind Daily Calculator's most used tools. Each guide explains the formula, works through a concrete example, and links to the calculators that put the formula into practice — so you can double-check any result and understand what it really means.
About calculation guides
A calculator can give you a number, but it cannot tell you whether the number makes sense in your situation. These guides fill that gap. They explain the reasoning behind a formula in plain language, walk through a real example, and point out the assumptions and edge cases that matter most.
Read one when you want to verify a result, reuse the formula in a spreadsheet, explain it to someone else, or simply satisfy your curiosity about how the maths works.
Math & Statistics Guides
Percentages, averages and the language of statistical spread.
How Percentages Work
Percent of a number, percentage change, percentage difference — with worked examples for each.
Read guide MathHow to Calculate Averages
Mean, median, mode and weighted average — how to compute each one and when to use it.
Read guide MathHow to Calculate Percentage Increase
Increase, decrease and the critical difference between percentage points and percentages.
Read guide MathHow to Interpret Standard Deviation
What SD actually measures, sample versus population formulas, and how to read the result.
Read guideFinance Guides
Interest, loan payments and how amortization actually works.
How Compound Interest Works
Compounding frequency, the compound interest formula, and why time beats rate for long-term growth.
Read guide FinanceHow to Calculate Loan Payments
The amortized payment formula step by step, plus how principal, rate and term interact.
Read guide FinanceHow to Use a Mortgage Amortization Schedule
Read an amortization table, see how each payment splits, and find where extra payments save the most.
Read guideHealth, Home & Everyday Guides
Body metrics, unit conversions and practical measurements.
How to Calculate BMI
The BMI formula in metric and imperial form, WHO categories, and the limitations to keep in mind.
Read guide ConvertersHow to Convert Temperature Units
Exact Celsius, Fahrenheit, Kelvin and Rankine formulas and why temperature is different from other conversions.
Read guide GeometryHow to Calculate Square Footage
Measure and calculate square footage for rooms, walls and irregular spaces — including L-shapes and cut-outs.
Read guideTry the Calculators Featured in the Guides
Each guide links to tools that apply the formulas it explains.
Percentage Calculator
Find a percent of a number, what percent one value is of another, and more.
Compound Interest Calculator
See how investments grow with compound interest over time.
BMI Calculator
Calculate body mass index in metric or imperial units.
Square Footage Calculator
Calculate square footage for rooms, floors and irregular spaces.
Guide FAQs
Each guide explains a formula and links to the calculators that use it. You can read a guide on its own or use it as a companion to a specific tool.
Yes. The guides are written in plain English with worked examples, so they work well as study aids alongside classroom material. Each one explains not just the formula but the reasoning behind it.
Yes — please use the contact page. We welcome suggestions for topics that would be helpful to explain.