Free Online Calculators & Converters
Fast, free, no-signup calculators for finance, business, and everyday math. Get an answer in one click. 23 tools and counting — no signup, no paywall, results as you type.
Business & Freelance
- Freelance Hourly Rate CalculatorWork out the hourly rate you need to charge to hit your target take-home income, after taxes, business expenses, unpaid time, and non-billable hours.
- Self-Employment Tax CalculatorCalculate 2026 self-employment tax on freelance or business income. Includes the 92.35% adjustment, the $184,500 Social Security cap, additional Medicare tax, and your deductible half.
Conversion & Trade
- Board Foot CalculatorCalculate board feet for any lumber dimensions, for one piece or a whole stack. Handles quarter sizing (4/4, 8/4), nominal vs actual thickness, and gives you the total cost.
- Gravel CalculatorCalculate how much gravel you need in cubic yards and tons. Handles driveways, patios, and circular areas, with compaction allowance and delivery truck loads.
- Mulch CalculatorWork out how much mulch you need in cubic yards and bags. Enter your bed size and depth to get volume, weight, delivery loads, and the cost of bulk versus bagged.
- Stair CalculatorCalculate stair risers, treads, total run, and stringer length from your floor-to-floor height. Checks every result against IRC riser and tread limits before you cut.
- Tile CalculatorCalculate how many tiles and boxes you need for a floor or wall, including waste for cuts and diagonal layouts. Gives grout, thinset, and total cost.
- Watts to Amps CalculatorConvert watts to amps for DC, single-phase AC, and three-phase AC. Enter voltage and power factor to get the exact current draw, plus the minimum breaker and wire size.
E-commerce
- Amazon FBA Fee CalculatorCalculate Amazon FBA fees, net profit, margin, and ROI for any product. Enter your price and cost to see referral fees, fulfillment fees, and your real take-home per unit.
- eBay Fee CalculatorCalculate eBay selling fees and your exact payout. Includes the 13.6% final value fee, per-order fee, international and ad fees, and shows what percentage of the sale eBay keeps.
- eBay Profit CalculatorWork out your real profit on an eBay sale after fees, cost of goods, shipping labels, packaging, and returns. Shows net margin, ROI, and the break-even selling price.
Math & Everyday
- Fraction CalculatorAdd, subtract, multiply, or divide two fractions and get the answer simplified, as a mixed number, and as a decimal. Handles mixed numbers as input too.
- Percentage Decrease CalculatorCalculate the percentage decrease between two numbers, apply a discount, or work backwards from a sale price to the original. Shows the arithmetic at each step.
- Percentage Increase CalculatorFind the percentage increase or decrease between two numbers instantly. Shows the percent change, the absolute difference, and the multiplier, with the formula worked out step by step.
- Sample Size CalculatorWork out how many survey responses you need for a given confidence level and margin of error, with finite population correction and the invitations to send.
- Scientific Notation CalculatorConvert any number to scientific notation, E notation, and engineering notation — or go the other way. Also multiplies and divides two numbers in scientific notation.
- Weighted Grade CalculatorCalculate your weighted course grade from category percentages. Shows your current average, your grade so far, and the final exam score you need to reach a target.
Personal Finance
- Credit Card Payoff CalculatorFind out how long it takes to clear a credit card balance and what the interest costs. Compare a fixed payment against a target payoff date, and see what minimum payments alone would cost you.
- Debt Snowball CalculatorSee your debt-free date with the snowball method. Enter up to five debts and an extra monthly payment to compare snowball vs avalanche vs minimum payments, month by month.
- Dividend Reinvestment CalculatorModel a DRIP over time: share count, portfolio value, annual dividend income, and yield on cost. Compare reinvesting dividends against taking them in cash, with taxes included.
- Mortgage Recast CalculatorCalculate your new mortgage payment after a lump-sum recast. Compare recasting against simply prepaying the same amount, and see the interest and years each option saves.
- Rule of 72 CalculatorEstimate how many years it takes to double your money at any rate of return, and see how far the Rule of 72 shortcut is from the exact answer. Works in reverse too.