What would you like to calculate?

Fast, free calculators for money, maths, health, time and everyday decisions. Every tool runs instantly in your browser — no sign-up, no clutter, and nothing you type leaves your device.

Popular calculators

• US Mortgage Calculator — Estimate the monthly repayment on a US home loan from the amount, rate and term, and see how an extra monthly payment shortens it.
• Loan Calculator — Work out repayments and total interest on any fixed-rate personal loan.
• Compound Interest Calculator — See how savings grow when interest earns interest, with optional monthly deposits.
• Percentage Calculator — Percentage of a number, one number as a percentage of another, and percentage change.
• Salary Calculator — Convert an annual salary into hourly, weekly and monthly pay, before and after US tax.
• BMI Calculator — Body mass index from height and weight, with the category it falls into.
• Age Calculator — Exact age in years, months and days, plus a countdown to the next birthday.
• Christmas Countdown — Live countdown to Christmas Day — months, weeks, days, hours, minutes and seconds to go, in your timezone.
• Date Calculator — Count the days, weeks and working days between any two dates.

Browse by category

• Money & Finance — Mortgages, loans, interest, salary and long-term planning maths, worked out in seconds.
• Health & Fitness — Body metrics, energy needs and everyday wellbeing numbers explained in plain language.
• Math & Science — Percentages, fractions, algebra, geometry and physics helpers for homework and work.
• Time & Date — Ages, gaps between dates, countdowns and time zone questions, answered exactly.
• Conversion — Switch between units of length, weight, temperature, volume and currency.
• Business & Productivity — Pricing, margin, break-even and return calculations for people running things.
• Household & Lifestyle — Rent, running costs, utilities and kitchen maths for the place you live in.
• Vehicle & Travel — Fuel economy, car finance and trip budgets before you turn the key.
• Education & Learning — Grades, averages and study finance tools for students and teachers.

Why CalculatorWonder

No sign-up, no clutter

Every calculator is free and works instantly. Nothing you type leaves your browser.

Explained, not just answered

Each page tells you the formula and the assumptions behind the number.

Hundreds more coming

We started with the essentials and expand the library from visitor requests.

Ready to work something out? Browse the money and finance tools or read the guides behind the numbers.