All calculators
Every tool on the site, grouped by category. Each calculator runs entirely in your browser and shows the exact formula, assumptions, and a worked example next to the result.
the complete calculator library brings the relevant tools and explanations together so you can move from a question to a result without hunting through unrelated material. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every item is written to show what the calculation means, which inputs matter, and where an estimate should not be treated as a guarantee.
A trustworthy result needs more than arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. This page therefore combines practical tools with formulas, worked reasoning, assumptions, limitations, and links to closely related material. You can use the result immediately while still having enough information to check it independently.
Start with the tool closest to the decision you need to make, enter values from a reliable source, and keep a copy of the assumptions that shaped the answer. If a small change in an input produces a large change in the outcome, compare several scenarios instead of relying on a single point estimate.
Finance
About finance calculators →- Mortgage CalculatorEstimate the monthly payment, total interest, and total cost of a fixed-rate mortgage.
- Loan CalculatorCalculate the monthly payment and total interest for any fixed-rate installment loan.
- Compound Interest CalculatorSee how an investment grows with compounding, with optional regular contributions.
- Simple Interest CalculatorCalculate simple (non-compounding) interest on a principal over time.
- Savings Goal CalculatorFind the monthly deposit needed to reach a savings goal by a target date.
- Percentage CalculatorFind what a percentage of a number is, what percent one number is of another, and the percentage change between two values.
- Percentage Increase CalculatorCalculate the percentage increase from a starting value to a new value, or apply an increase directly.
- Percentage Decrease CalculatorCalculate the percentage decrease between two values, or reduce a number by a given percentage.
- Average CalculatorCalculate the arithmetic mean of a set of numbers, along with the count, sum, minimum, and maximum.
- Fraction CalculatorAdd, subtract, multiply, and divide fractions, with results simplified to lowest terms and shown as mixed numbers.
- Ratio CalculatorSimplify a ratio to its lowest terms and see the equivalent proportion per unit.
- Exponent CalculatorRaise any base to any power, including negative and fractional exponents.
- Square Root CalculatorFind the square root of any non-negative number, and check whether it is a perfect square.
- Quadratic Equation CalculatorSolve ax² + bx + c = 0 with the quadratic formula, including the discriminant and complex roots.
- BMI CalculatorCalculate body mass index from height and weight, in metric or imperial units, with the WHO classification.
- BMR CalculatorEstimate basal metabolic rate — the calories your body burns at rest — using the Mifflin–St Jeor equation.
- TDEE CalculatorEstimate total daily energy expenditure — maintenance calories — from BMR and activity level.
Time & Date
About time & date calculators →- Age CalculatorCalculate an exact age in years, months, and days between a date of birth and any date.
- Date Difference CalculatorCount the days, weeks, months, and years between two calendar dates.
- Date Add / Subtract CalculatorAdd or subtract years, months, weeks, and days from any date.
- Business Days CalculatorCount working days (Monday–Friday) between two dates, excluding weekends.
Everyday
About everyday calculators →- Tip CalculatorWork out the tip, total bill, and per-person split for any check.
- Discount CalculatorFind the sale price and savings after a percentage discount.
- Grade CalculatorConvert points earned into a percentage and a letter grade.
- Fuel Cost CalculatorEstimate the fuel needed and total cost of a trip from distance, fuel economy, and price per gallon.
Choosing the right tool
Begin by stating the question in ordinary language before choosing a calculator or guide. the complete calculator library is most useful when the result supports a clear decision rather than standing alone as an unexplained number. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. The practical check is to identify the inputs, keep units and time periods consistent, calculate with more precision than the final answer needs, and then ask whether the result is plausible in context. This approach catches entry errors, prevents false confidence, and makes the answer easier to explain to another person.
A useful workflow is to write down the intended outcome, verify each source value, run a baseline case, and then test a realistic high and low case. For the complete calculator library, that process gives the result a defensible range and makes uncertainty visible. It also prevents a neat-looking output from hiding a weak assumption. When the stakes are high, retain the original source and note why each input was selected.
Understanding the inputs
Inputs should come from current documents, measurements, or clearly stated assumptions rather than memory where accuracy matters. the complete calculator library is most useful when the result supports a clear decision rather than standing alone as an unexplained number. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. The practical check is to identify the inputs, keep units and time periods consistent, calculate with more precision than the final answer needs, and then ask whether the result is plausible in context. This approach catches entry errors, prevents false confidence, and makes the answer easier to explain to another person.
A useful workflow is to write down the intended outcome, verify each source value, run a baseline case, and then test a realistic high and low case. For the complete calculator library, that process gives the result a defensible range and makes uncertainty visible. It also prevents a neat-looking output from hiding a weak assumption. When the stakes are high, retain the original source and note why each input was selected.
Keeping units consistent
Many apparently wrong results come from mixing percentages and decimals, monthly and annual periods, or metric and customary units. the complete calculator library is most useful when the result supports a clear decision rather than standing alone as an unexplained number. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. The practical check is to identify the inputs, keep units and time periods consistent, calculate with more precision than the final answer needs, and then ask whether the result is plausible in context. This approach catches entry errors, prevents false confidence, and makes the answer easier to explain to another person.
A useful workflow is to write down the intended outcome, verify each source value, run a baseline case, and then test a realistic high and low case. For the complete calculator library, that process gives the result a defensible range and makes uncertainty visible. It also prevents a neat-looking output from hiding a weak assumption. When the stakes are high, retain the original source and note why each input was selected.
Reading the result
Separate the main answer from supporting totals, rates, dates, or ranges so the number is not interpreted outside its intended meaning. the complete calculator library is most useful when the result supports a clear decision rather than standing alone as an unexplained number. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. The practical check is to identify the inputs, keep units and time periods consistent, calculate with more precision than the final answer needs, and then ask whether the result is plausible in context. This approach catches entry errors, prevents false confidence, and makes the answer easier to explain to another person.
A useful workflow is to write down the intended outcome, verify each source value, run a baseline case, and then test a realistic high and low case. For the complete calculator library, that process gives the result a defensible range and makes uncertainty visible. It also prevents a neat-looking output from hiding a weak assumption. When the stakes are high, retain the original source and note why each input was selected.
Checking the calculation
Estimate the order of magnitude first, then reproduce a simplified version by hand or with an independent method. the complete calculator library is most useful when the result supports a clear decision rather than standing alone as an unexplained number. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. The practical check is to identify the inputs, keep units and time periods consistent, calculate with more precision than the final answer needs, and then ask whether the result is plausible in context. This approach catches entry errors, prevents false confidence, and makes the answer easier to explain to another person.
A useful workflow is to write down the intended outcome, verify each source value, run a baseline case, and then test a realistic high and low case. For the complete calculator library, that process gives the result a defensible range and makes uncertainty visible. It also prevents a neat-looking output from hiding a weak assumption. When the stakes are high, retain the original source and note why each input was selected.
Comparing scenarios
Change one assumption at a time and record the effect, which reveals which inputs genuinely drive the outcome. the complete calculator library is most useful when the result supports a clear decision rather than standing alone as an unexplained number. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. The practical check is to identify the inputs, keep units and time periods consistent, calculate with more precision than the final answer needs, and then ask whether the result is plausible in context. This approach catches entry errors, prevents false confidence, and makes the answer easier to explain to another person.
A useful workflow is to write down the intended outcome, verify each source value, run a baseline case, and then test a realistic high and low case. For the complete calculator library, that process gives the result a defensible range and makes uncertainty visible. It also prevents a neat-looking output from hiding a weak assumption. When the stakes are high, retain the original source and note why each input was selected.
Rounding and precision
Keep full precision during intermediate steps and round only the displayed answer to the level the decision can support. the complete calculator library is most useful when the result supports a clear decision rather than standing alone as an unexplained number. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. The practical check is to identify the inputs, keep units and time periods consistent, calculate with more precision than the final answer needs, and then ask whether the result is plausible in context. This approach catches entry errors, prevents false confidence, and makes the answer easier to explain to another person.
A useful workflow is to write down the intended outcome, verify each source value, run a baseline case, and then test a realistic high and low case. For the complete calculator library, that process gives the result a defensible range and makes uncertainty visible. It also prevents a neat-looking output from hiding a weak assumption. When the stakes are high, retain the original source and note why each input was selected.
Assumptions and limitations
A formula models selected features of reality and necessarily leaves out details that may matter in a particular case. the complete calculator library is most useful when the result supports a clear decision rather than standing alone as an unexplained number. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. The practical check is to identify the inputs, keep units and time periods consistent, calculate with more precision than the final answer needs, and then ask whether the result is plausible in context. This approach catches entry errors, prevents false confidence, and makes the answer easier to explain to another person.
A useful workflow is to write down the intended outcome, verify each source value, run a baseline case, and then test a realistic high and low case. For the complete calculator library, that process gives the result a defensible range and makes uncertainty visible. It also prevents a neat-looking output from hiding a weak assumption. When the stakes are high, retain the original source and note why each input was selected.
Using sources responsibly
Definitions and conversion factors should come from primary standards or recognized professional bodies whenever possible. the complete calculator library is most useful when the result supports a clear decision rather than standing alone as an unexplained number. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. The practical check is to identify the inputs, keep units and time periods consistent, calculate with more precision than the final answer needs, and then ask whether the result is plausible in context. This approach catches entry errors, prevents false confidence, and makes the answer easier to explain to another person.
A useful workflow is to write down the intended outcome, verify each source value, run a baseline case, and then test a realistic high and low case. For the complete calculator library, that process gives the result a defensible range and makes uncertainty visible. It also prevents a neat-looking output from hiding a weak assumption. When the stakes are high, retain the original source and note why each input was selected.
Avoiding common mistakes
Do not reverse the starting and ending value, overlook an included fee, or assume a default applies everywhere. the complete calculator library is most useful when the result supports a clear decision rather than standing alone as an unexplained number. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. The practical check is to identify the inputs, keep units and time periods consistent, calculate with more precision than the final answer needs, and then ask whether the result is plausible in context. This approach catches entry errors, prevents false confidence, and makes the answer easier to explain to another person.
A useful workflow is to write down the intended outcome, verify each source value, run a baseline case, and then test a realistic high and low case. For the complete calculator library, that process gives the result a defensible range and makes uncertainty visible. It also prevents a neat-looking output from hiding a weak assumption. When the stakes are high, retain the original source and note why each input was selected.
Documenting a decision
Record the date, source values, formula, and chosen scenario when the result will be used later or shared with somebody else. the complete calculator library is most useful when the result supports a clear decision rather than standing alone as an unexplained number. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. The practical check is to identify the inputs, keep units and time periods consistent, calculate with more precision than the final answer needs, and then ask whether the result is plausible in context. This approach catches entry errors, prevents false confidence, and makes the answer easier to explain to another person.
A useful workflow is to write down the intended outcome, verify each source value, run a baseline case, and then test a realistic high and low case. For the complete calculator library, that process gives the result a defensible range and makes uncertainty visible. It also prevents a neat-looking output from hiding a weak assumption. When the stakes are high, retain the original source and note why each input was selected.
When to seek specialist help
Educational tools support planning but cannot replace a qualified professional where health, law, tax, credit, or safety is involved. the complete calculator library is most useful when the result supports a clear decision rather than standing alone as an unexplained number. The directory groups tools by the kind of question they answer, from percentages and loans to calorie estimates and calendar arithmetic. Every listing leads to an interactive calculator whose inputs, formula, result, assumptions, and examples can be reviewed together. The practical check is to identify the inputs, keep units and time periods consistent, calculate with more precision than the final answer needs, and then ask whether the result is plausible in context. This approach catches entry errors, prevents false confidence, and makes the answer easier to explain to another person.
A useful workflow is to write down the intended outcome, verify each source value, run a baseline case, and then test a realistic high and low case. For the complete calculator library, that process gives the result a defensible range and makes uncertainty visible. It also prevents a neat-looking output from hiding a weak assumption. When the stakes are high, retain the original source and note why each input was selected.
Frequently asked questions
- What is the best way to use the complete calculator library?
- Define the decision first, choose the closest tool, verify the inputs, and read the result together with its assumptions and limitations. A result is most valuable when you can explain where every number came from and reproduce the method independently.
- How accurate are the results on the complete calculator library?
- The arithmetic follows the formulas shown, but practical accuracy depends on the values entered and on how well the model represents the real situation. Use current source values and compare scenarios when an input is uncertain.
- Why should I compare more than one scenario?
- A single answer can hide how sensitive the outcome is. A baseline, lower case, and upper case show the reasonable range and identify which assumption has the greatest effect on the decision.
- When should I round the answer?
- Keep full precision during the calculation and round only the final displayed result. Match the rounding to the measurement and decision; extra decimal places do not create extra certainty.
- How can I check whether an answer is reasonable?
- Estimate the size and direction before calculating, check units, repeat a simplified version by hand, and compare with a second method or a known reference point. Large disagreements usually reveal a unit or input error.
- Are these tools a substitute for professional advice?
- No. They provide general educational estimates. Decisions involving health, regulated finance, tax, law, or safety should be checked with a suitably qualified professional who can consider the complete situation.
- What information should I save with a result?
- Save the date, every input and its source, the formula or tool used, the displayed result, and any assumptions. That record makes future review and comparison much easier.
- Why can another calculator show a different answer?
- Tools may use different defaults, conventions, rounding rules, time periods, or formulas. Compare their stated assumptions before deciding that either answer is wrong.