Free math tools
Free calculators and drills for business math and mental math. Each one shows the formula, a worked example from a checked Doing Math lesson, and three problems to try. Nothing to install, no sign-up, and nothing you type leaves your browser.
Mental math
- Mental math speed drillA free, timed mental arithmetic drill: 60 or 120 seconds of +, −, × and ÷, plus Business %, Squares and 80-in-8 presets. No sign-up.
- 80 in 8 practicePractice the 80 in 8 format for trading interviews: 80 mental arithmetic questions in 8 minutes, with decimals. Free, no sign-up.
- Mental math tricks13 techniques for doing sums in your head, each with steps, a worked example and three to try.
Business
- Markup vs margin calculatorEnter any two of cost, price, markup and margin to get the rest. A $60 item that costs $40: 50% markup, 33.3% margin. Free, no sign-up.
- Profit margin calculatorGross, operating and net profit margin from revenue and costs. Each margin is that profit line divided by revenue. Free, no sign-up.
- Break-even calculatorBreak-even units and sales revenue from fixed costs, price and variable cost per unit, with a target-profit mode. Free, no sign-up.
- Contribution margin calculatorContribution margin per unit and ratio, total contribution, operating profit and operating leverage from price, variable cost and fixed costs.
Percents
- Percent change calculatorPercent increase or decrease from an old and a new value, percent difference, percentage points, and the value before a change. Free, no sign-up.
- Decimal to fraction converterTurn a decimal into a fraction in lowest terms, a fraction into a decimal, and both into a percent, with the steps and a printable chart.
- Percent off calculatorThe price after a discount, two stacked discounts (20% then 10% is not 30%), and the price before sales tax. Free, no sign-up.
Finance
- Rule of 72 calculatorHow long money takes to double: the rule of 72, the rule of 70 and the exact answer, with a table of how far the rule drifts. Free, no sign-up.
- CAGR calculatorThe compound annual growth rate from a start value, an end value and the years, plus the end value at a steady rate. Free, no sign-up.