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Formulas, verified before they ship

Paycheck, GPA, BMI, concrete.
Every one, worked out in full.

Mortgages, paychecks, macros, and concrete mix. A growing library of precise, well-built calculators, no signup, no paywall, no clutter.

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AP Calculus AB Score Calculator

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Fantasy Points Calculator

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Gravel Calculator

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Compound Interest Calculator

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457(b) Contribution Limit Calculator

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BMI Calculator

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Browse all 87 calculators
The full list

Every calculator, all 87 of them.

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18 worlds to explore.

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About

What CalculatorPlanet is

CalculatorPlanet is a free library of calculators built one category at a time, covering tax and salary, academics, finance, health, construction, science and math, agriculture, gaming and more. Each calculator answers one specific question and shows the formula behind the number, not just the number itself. There is no account, no paywall and nothing to sign up for.

How it works

How a result gets to you

  1. 01

    Enter your numbers

    Type in the values a calculator asks for. Nothing else is required.

  2. 02

    See the verified formula

    Every calculator shows the actual formula it uses, written in plain English.

  3. 03

    Check it against a worked example

    A real example is worked out by hand and checked against the live calculation before a calculator ships.

  4. 04

    Use it free, no account

    No sign up, no paywall and no limit on how many times you calculate.

Categories

What you can calculate

  • Tax and salary

    Paycheck withholding by state, self employment tax, and HSA or 457(b) contribution limits.

  • Academic

    GPA, weighted grades, the score you need on a final, and AP Calculus AB score estimates.

  • Health

    Body mass index and daily calorie needs based on activity level.

  • Construction

    Gravel, crushed stone and river rock, estimated by the ton or the cubic yard.

  • Finance

    Compound interest growth and monthly loan payments.

  • Science and math

    Percentages and temperature conversions between Celsius, Fahrenheit and Kelvin.

  • Agriculture

    Corn yield estimates and gestation dates for dogs, goats and horses.

  • Others

    Fantasy football scoring, sports betting odds, sewing yardage, pool salt levels and more.

Field notes

The reasoning, written out.

H

How Age Calculators Handle Leap Years

Exact age math looks trivial until a leap-year birthday or month-end date hits. Here's the calendar math an accurate age calculator runs.

8 min · Aug 2026Read
H

How Percentages Actually Work — And How They Get Misread

Percentages compare a part to a whole, but the same true number can be framed to look alarming or trivial. Here's how to read one correctly.

10 min · Aug 2026Read
All articles
Questions

Frequently asked questions

What is CalculatorPlanet?

CalculatorPlanet is a free collection of online calculators covering tax and salary, academics, health, finance, construction and more. Every calculator explains the formula it uses and works through a real example, not just a bare number.

Are the calculators free to use?

Yes. Every calculator on the site is free, with no paywall and no limit on how many times you use it.

Do I need to create an account?

No. None of the calculators require a sign up, a login or an email address to use.

How accurate are the results?

Each calculator uses a documented formula that is checked against a worked example before it ships. Where a figure is not pure arithmetic, such as a tax rate or a medical threshold, the source and the date it was checked are listed on the page.

Can I use CalculatorPlanet on my phone?

Yes. Every calculator is built to work on a phone, tablet or desktop browser without installing anything.

Where can I see every calculator?

The full calculator directory lists every tool on the site grouped by category, and the search bar at the top of any page finds a specific calculator by name.

Is Calculator Planet the same site as CalculatorPlanet?

Yes. CalculatorPlanet and Calculator Planet refer to the same site. The name is written as one word throughout the site and in the web address.