Math and Statistics

  • Percent Efficiency Calculator
    Calculate percent efficiency from useful output and total input energy. Free online efficiency calculator using output/input × 100, with energy loss.
  • A/B Test Significance Calculator
    Check if your A/B test result is statistically significant. Enter visitors and conversions for each variant to get Z-score, p-value, uplift, and a verdict.
  • Lottery Expected Value Calculator
    Calculate the expected value of a lottery ticket from the jackpot, odds, and ticket price. See if a ticket is worth it in the long run.
  • D&D Advantage / Disadvantage Dice Calculator
    Calculate your chance to hit a d20 target number with Advantage, Disadvantage, or a normal roll in Dungeons & Dragons 5e.
  • Solve and Graph Inequalities Calculator
    Solve linear inequalities ax + b ≤ c (and <, ≥, >) instantly. Get the boundary value, direction, and interval notation for the number line.
  • Long Division Calculator
    Free long division calculator: enter a dividend and divisor to get the quotient, remainder, and decimal result instantly using a = b·q + r.
  • Round to n Significant Figures Calculator
    Round any number to a chosen number of significant figures and view its scientific-notation form (mantissa and exponent). Free, instant, and accurate.
  • Solve for y Calculator
    Solve for y in a linear equation Ax + By = C. Enter A, B, C and x to instantly isolate y, plus get the slope and y-intercept. Free online tool.
  • Tax as Percent of Income Calculator
    Find what percent of your gross income goes to tax. Enter total tax paid and income to get your effective tax rate and take-home percent instantly.
  • Multi-Step Equation Calculator
    Solve linear equations of the form ax + b = cx + d for x. Enter the four coefficients and get the exact step-by-step solution instantly.
  • Simple Interest Percentage (Rate) Calculator
    Find the simple interest rate as a percentage from principal, interest earned, and time. Rate = (I / (P x T)) x 100. Free, instant, accurate.
  • Occupancy Rate Calculator
    Calculate occupancy rate as a percentage for hotels, rentals, parking, and venues. Enter occupied and total units to get occupancy and vacancy %.
  • Law of Total Probability Calculator
    Compute P(A) from conditional and partition probabilities using the law of total probability: P(A) = Σ P(A|Bᵢ)·P(Bᵢ). Supports up to 3 events.
  • Polynomial from Roots Calculator
    Build and expand a polynomial P(x) from its real roots. Enter zeros and a leading coefficient to get the full expanded form, degree, and constant term.
  • Simplify Fraction Calculator
    Simplify any fraction to its lowest terms using the greatest common factor (GCF). Get the reduced fraction, GCF, decimal value, and mixed number instantly.
  • Average Speed Calculator (Two Trips)
    Calculate average speed across two trips using total distance divided by total time. Enter distances and times to get the true overall speed.
  • Percent of Goal Achieved Calculator
    Calculate the percent of goal achieved (quota attainment) by dividing actual by target. See attainment %, amount remaining, and % left to goal.
  • Percent of Budget Spent Calculator
    Find what percentage of your budget you have spent. Enter your total budget and amount spent to see percent used, percent remaining, and money left.
  • Parallel or Perpendicular Lines Checker
    Check if two lines are parallel, perpendicular, or neither by comparing their slopes. Enter m₁ and m₂ to get an instant answer with the product.
  • Average of Two Numbers (Midpoint Value) Calculator
    Find the average (midpoint) of two numbers instantly with average = (a + b) / 2. Also shows the amplitude (half-range) between the values.
  • Probability of Rolling a Specific Sum Calculator
    Find the exact probability of rolling a chosen sum with any number of dice and sides. Uses convolution counting: P = (ways to make sum) / sides^n.
  • Cumulative Binomial Probability Calculator
    Compute cumulative binomial probability P(X≤k) for n trials with success probability p. Also returns P(X=k), P(X>k), P(X≥k) and the mean.
  • Probability X Greater Than a Value (Normal Distribution)
    Compute P(X > x) for a normal distribution from mean, standard deviation, and a value. Returns the right-tail probability, z-score, and percentage.
  • 401(k) Contribution Percentage Calculator
    US 401(k) calculator: enter your salary and deferral percentage to see your annual and per-paycheck retirement contribution amounts.

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