Free online calculators, done properly
20 fast, accurate tools for money, health, and everyday life — each one explained, so you understand the answer, not just get it.
QuickSum is a collection of twenty purpose-built calculators covering the questions that actually come up: what a loan really costs, whether your mortgage budget is realistic, how many calories you need, what your money could grow into, and the quick conversions in between. Every tool runs entirely in your browser — nothing you type is ever sent to a server — and every calculator page explains the formula behind it, walks through a worked example, and answers the questions people most often ask.
Not sure where to start? The loan, BMI, and currency calculators are our most used — or browse the full collection below.
100% privateAll maths runs in your browser. Your inputs never leave your device.
Explained, not just computedEach tool shows its formula, a worked example, and honest caveats.
Free, no signupNo accounts, no paywalls, no limits — on any device.
Finance calculators
Loans, mortgages, savings, taxes, and retirement — see the full cost or the full growth before you commit.
💰Loan calculatorMonthly payment, total repayment, and lifetime interest for any fixed-rate loan.
🏠Mortgage calculatorFull monthly payment with principal, interest, property tax, and insurance.
%Interest calculatorSimple vs compound interest, side by side, at any compounding frequency.
🧾Tax calculatorUS federal income tax, effective rate, and monthly take-home pay.
💼Salary calculatorConvert pay between hourly, weekly, monthly, and annual equivalents.
📈Investment calculatorProject growth from a lump sum plus monthly contributions.
💳Credit card payoff calculatorMonths to debt-free and total interest at your monthly payment.
🏖Retirement calculatorNest egg at retirement and the monthly income it could fund.
Health calculators
Quick, evidence-based estimates for BMI, calories, body composition, and training zones.
Everyday calculators
The conversions and quick sums that come up all the time — currency, units, dates, tips, and more.
🧮Standard calculatorA clean, fast basic calculator for everyday arithmetic.
💲Currency calculatorConvert 15 major currencies with live ECB reference rates.
📐Unit calculatorLength, weight, temperature, volume, speed, and data units.
🏷Discount / tip calculatorSale price after discount, tip, and per-person bill splits.
🎂Age calculatorExact age in years, months, and days, plus birthday countdown.
📅Date difference calculatorDays, weeks, and business days between any two dates.
🚀Speed / distance calculatorEnter any two of speed, distance, and time — solve the third.
📦Area calculatorArea of rectangles, circles, triangles, and trapezoids.
From the blog
Guides that go deeper than the numbers. See all articles →