ProCalcHub Blog
Practical guides to everyday calculations — loans and mortgages, margins and VAT, percentages, BMI, dates and unit conversions. Each guide explains the method, the formula and a worked example.
Calculator guides
Each guide explains how a calculator works, the formula behind it and a worked example.
Business & Finance
- Loan Calculator — Work out the fixed monthly payment on a personal loan, car loan or any amortizing loan, and see how much of what you pay goes to interest over the life of the loan.
- Margin Calculator — Find your gross margin and markup from cost and selling price, or work backwards from a target margin to the price you need to charge.
- Mortgage Calculator — Estimate the full monthly cost of a home loan — principal and interest plus property tax, homeowners insurance and HOA dues — and see how the loan pays down over time.
- ROI Calculator — Measure how much an investment gained or lost relative to its cost, and compare investments held for different lengths of time with annualized ROI.
- VAT Calculator — Add VAT to a net price or extract it from a VAT-inclusive price. The same maths works for sales tax and GST at any rate.
Unit Conversion
- Currency Converter — Convert between 30 major world currencies using the European Central Bank's published reference rates (latest: 2026-09-11).
- Unit Converter — Convert between metric, imperial and US customary units for length, weight, temperature, area, volume, speed, time and digital storage — with the exact formula for every conversion.
Math & Algebra
- Percentage Calculator — Solve the everyday percentage questions — what is X% of Y, X is what percent of Y, the percentage change between two values, and a value increased or decreased by a percentage — with every step shown.
- Quadratic Equation Solver — Solve ax² + bx + c = 0 with the quadratic formula. Enter the three coefficients to get the roots — real or complex — along with the discriminant, vertex and every step.
Date & Time
- Date Difference Calculator — Count the exact number of days between two dates and see the same span in years, months and days, weeks, business days and hours.
Health & Fitness
- BMI Calculator — Calculate your body mass index from your height and weight, see which WHO category it falls in and the healthy weight range for your height.
Text & Data
- Password Generator — Create strong, random passwords with the length and character types you need. Passwords are generated on your device using cryptographically secure randomness and never leave your browser.