Math Tools

Calculate exact age from a date of birth in years, months and days, plus total days lived and the next birthday countdown.

Calculate area and volume for common shapes with the formulas shown, plus the unit and rounding traps that cause real errors.

Apply Bayes theorem to update a prior probability with test evidence, showing the false positive paradox in natural frequencies alongside the algebra.

Perform exact arithmetic on integers of any size with no precision loss: addition, multiplication, division with remainder, powers, factorials, GCD and base conversion.

Do arithmetic and bitwise operations on two binary numbers and see the result in binary, decimal and hexadecimal at once. Runs in your browser.

Compute exact binomial probabilities for any number of trials and success probability, with cumulative values, the full distribution table and a check on whether the normal approximation applies.

Estimate your blood alcohol content (BAC) from the number of standard drinks, body weight, sex and time elapsed, using the Widmark formula. For education only. Private.

Check your blood pressure category (normal, elevated, hypertension stage 1/2, crisis) from your systolic and diastolic readings, per AHA guidelines. Educational, private.

Calculate body mass index from height and weight in metric or imperial units, with the WHO categories and an honest account of BMI's limits.

Calculate BMI using common Indian units (kg + feet/inches). Shows BMI category.

Estimate basal metabolic rate and total daily energy expenditure, with the equations, activity multipliers and their real accuracy.

Estimate your body fat percentage using the trusted US Navy circumference method from your height, neck, waist (and hip) measurements. Free, private, instant.

Calculate body surface area (BSA) from height and weight using the Mosteller and Du Bois formulas, widely used in medicine and dosing. Free, private, instant.

Calculate your daily calorie needs (TDEE) to maintain, lose or gain weight, using the accurate Mifflin-St Jeor equation and your activity level. Free, private, instant.

Estimate calories burned for running, walking, cycling, swimming and many activities using MET values, your weight and duration. Free, private, instant.

Run a chi-square test of independence on a contingency table or a goodness of fit test against expected frequencies, with expected counts, residuals, effect size and assumption checks.

Calculate arc length, chord length, sector area, segment area and the sagitta of a circle from any two known measurements, with degrees and radians throughout.

Add, multiply, divide and exponentiate complex numbers, convert between rectangular and polar form, and find all n-th roots with the principal value clearly marked.

Calculate confidence intervals for a mean, a proportion or a difference between two groups, using the t distribution for small samples and the Wilson interval for proportions.

Calculate Pearson, Spearman and Kendall correlation from paired data, with significance testing, confidence intervals and a scatter plot showing what the number is actually measuring.

Calculate the exact number of days, weeks, months and working days between two dates, with leap years handled correctly.

Convert decimals to fractions in lowest terms, including repeating decimals converted exactly.

Differentiate an expression symbolically with the product, quotient and chain rules applied and named at each step, plus higher derivatives and evaluation at a point.

Compute the exact probability distribution for any dice pool including modifiers, advantage, keep highest or lowest, exploding dice and target numbers.

Find where a function crosses zero using bisection, Newton-Raphson and the secant method, with automatic bracketing, convergence history and a comparison of the three methods.

Calculate expected value, variance and standard deviation from a list of outcomes and probabilities, with a check that the probabilities sum to one and the long-run behaviour explained.

Calculate powers and roots, and apply the exponent rules without the sign and order errors.

Calculate factorials of any size, and understand where they come from and how fast they grow.

Generate the Fibonacci sequence up to a specific number or N terms.

Calculate with fractions and mixed numbers, with each step shown and results reduced to lowest terms.

Convert fractions to decimals, and see which ones terminate, which repeat, and why.

Plot up to three functions on shared axes with automatic scaling, and find the roots, turning points, intersections and asymptotes visible in the window.

Find the greatest common divisor and least common multiple of any set of numbers, with the method shown.

Calculate remaining quantity after radioactive or exponential decay from half-life and elapsed time, plus decay constant and mean lifetime.

Perform mathematical operations on hex values.

Calculate your ideal body weight from height and sex using the Devine, Robinson, Miller and Hamwi formulas, plus a healthy BMI range. Free, private, instant.

Interpolate between known data points using linear, Lagrange polynomial and cubic spline methods, with the differences between them shown and extrapolation flagged.

Calculate your lean body mass (LBM) and fat mass from weight, height and sex using the Boer formula. Useful for fitness, dosing and nutrition. Free, private, instant.

Convert between metres, feet, inches, miles, kilometres and more, with the precision and rounding issues that cause real errors.

Solve systems of linear equations with Gaussian elimination and partial pivoting, showing each row operation, the determinant, and whether the system has one solution, none or infinitely many.

Calculate logarithms in any base, and understand what a log actually answers.

Divide whole numbers with full step-by-step long division working, quotient, remainder and decimal result.

Perform matrix addition, subtraction, multiplication, determinant, and transpose operations.

Calculate your maximum heart rate and personalized training zones (fat burn, cardio, peak) using your age and resting heart rate (Karvonen method). Free, private.

Find the midpoint between two points with the midpoint formula, plus distance and slope, with a live coordinate plot.

Compute modular addition, multiplication, exponentiation by squaring, the modular inverse by the extended Euclidean algorithm, and solve systems with the Chinese remainder theorem.

Calculate the modulo of any two numbers, with the negative-operand behaviour that differs between languages.

Calculate normal distribution probabilities, z-scores, percentiles and critical values with a high-accuracy error function, for any mean and standard deviation.

Generate arithmetic and geometric number sequences from a starting value, step or ratio and term count, with the sum of the series. Great for math and testing. Private.

Convert numerals into written English words for cheques, contracts and documents, in short or long scale.

Compute a definite integral numerically with the trapezoid rule, Simpson rule, Romberg extrapolation and Gauss-Legendre quadrature, comparing the methods and estimating the error.

Calculate percentages, percentage change, increase and decrease, and reverse percentages, with the working shown for each result.

Calculate percentiles and percentile rank from a dataset, and understand why tools disagree about the answer.

Calculate Poisson probabilities for counts of events in a fixed interval, with cumulative values, the distribution table and a check of whether the constant rate assumption is plausible.

Find every root of a polynomial of any degree using the Durand-Kerner method, with real and complex roots, multiplicity detection, and the residual at each root.

Find the prime factorisation of any number, and see why it is unique and what it is used for.

Check whether a number is prime, see its factors if it isn't, and find the next and previous prime numbers. Handles large numbers efficiently. Free, private, instant.

Calculate probabilities for single and combined events, including conditional probability and Bayes' theorem.

Solve for any side of a right triangle, plus distance between points and diagonal measurements.

Solve any quadratic equation, with the discriminant, the roots and the vertex shown and explained.

Multiply, normalise and invert quaternions, convert between quaternions, axis-angle and Euler angles, and rotate a vector, with gimbal lock detected and explained.

Simplify ratios, solve proportions and split a total by ratio, without the part-to-whole confusion.

Calculate every measurement of a regular polygon from any one of them: side length, area, perimeter, apothem, circumradius, interior and exterior angles, and diagonal count.

Convert between Arabic numbers and Roman numerals, following the subtractive rules correctly.

Convert between roof pitch (x/12), angle in degrees and slope percentage, with rafter length factor and a live diagram.

Round numbers to decimal places, significant figures or any interval, using the rounding mode you actually need.

Calculate your running pace per km and per mile, plus speed, from a distance and time. Includes splits for 5K, 10K, half and full marathon. Free, private, instant.

Perform advanced mathematical operations including trig, log, and exponents.

Convert between decimal and scientific notation, including engineering notation and significant figures.

Count the significant figures in any number and round values to a chosen number of sig figs, with the rules explained.

Calculate the slope between two points, convert between gradient, percentage and degrees, and get the line equation.

Calculate how much smoking costs you per day, month, year and over 10 years, based on cigarettes per day and pack price. A powerful motivator to quit. Free, private.

Calculate square roots exactly where possible, in simplified radical form, and as decimals otherwise.

Calculate standard deviation, variance and mean, with the population-versus-sample distinction that changes the answer.

Calculate mean, median, mode, standard deviation, and more.

Calculate basic statistical values from a dataset.

Convert your daily step count into calories burned and distance walked, based on your weight and stride. A great companion to your fitness tracker. Free, private.

Run a one sample, two sample or paired t-test with exact p-values, Welch correction, effect size, confidence interval and an explanation of what the result does and does not show.

Convert between Celsius, Fahrenheit and Kelvin with the formulas, key reference points and the difference between a temperature and a difference.

Calculate a tip at any percentage, split a bill between any number of people, and handle tax and rounding correctly.

Solve a triangle from any valid combination of sides and angles using the sine and cosine rules, with the ambiguous case detected and both solutions given when two exist.

Calculate vector addition, dot and cross products, magnitude, unit vectors, the angle between vectors, projection and the scalar triple product in two or three dimensions.

Calculate your waist-to-hip ratio (WHR) and see your associated health risk category by sex, per WHO guidelines. Free, private, instant.

Convert between kilograms, pounds, stone, ounces and grams, including the stone-and-pounds format used in the UK and Ireland.

Convert English number words back into digits (e.g. 'two thousand twenty-four' → 2024). Handles tens, hundreds, thousands, millions and billions. Private & instant.