Free Online Calculators That Just Work

Mortgage payments, BMI, retirement projections, percentage problems. MSO Calc gives you 53 calculators plus a long-form guide for every one. Run the numbers, then read the math behind them.

53 Calculators 53 In-Depth Guides 100% Free No Sign-Up Mobile-Friendly
Ad Slot — Top Banner
📖

Read the math behind every number

53 long-form guides explaining what each calculator actually does.

Every calculator on this site comes with a companion guide. Want to know whether to take a 15-year mortgage instead of a 30-year? Read the mortgage basics guide. Confused why your BMI says one thing and your gym scale says another? The BMI guide walks through what the formula misses. Stuck on percentage word problems? The percentages guide shows the five patterns that cover almost every question.

Browse all guides →

Why MSO Calc?

You came here for a number. We get that. So the calculators load fast, the math is transparent, and the results come up in real time as you type. No paywalls, no email capture, no upsell to a financial product. Every calculation runs in your browser, so your inputs never leave your device.

A Calculator for Every Decision (Plus a Guide for the Why)

Personal finance, fitness, schoolwork, home improvement. There is a moment in almost every project where you stare at a question and think "how do I work this out?" MSO Calc covers the most common ones: monthly mortgage payments, BMI, compound interest, percentage problems, unit conversion, your exact age, and dozens more. Each calculator pairs with a 1,000-to-2,000-word guide that explains the formula, walks through a worked example, and lists the FAQs people actually ask.

Built for Accuracy

The formulas behind these calculators are the same ones used in textbooks, financial industry software and government agencies. We use the standard time-value-of-money formulas for finance, the Mifflin-St Jeor equation for BMR, the Heron formula for triangle area, and so on. You can read the math on each page. That said: calculators are tools, not advisors. Always double-check important numbers and consult a qualified professional before making a major decision.

Multi-Currency Support

Financial calculators include a currency selector — USD, EUR, GBP, CHF, JPY, CAD, AUD and INR — so you can see results in the currency you actually use. The displayed amounts use proper locale-aware formatting (decimal points, thousand separators, symbol placement) thanks to your browser's built-in internationalization API.

Privacy-First by Design

There's no account to create, no login screen, no tracking pixel that follows you around the internet. Your inputs stay in your browser; we never see them. We display advertisements (so we can keep the site free) and use lightweight analytics to understand which calculators people find most useful — but that's it. Full details in our privacy policy.