Every calculator

Mortgages, loans, cards, savings and the arithmetic of what things really cost.

• $Money

  Compound interest calculator: how a balance and deposits grow

  A starting balance and a stream of deposits grow under two different formulas. This page works both out by hand and shows what the rate, the term and the frequency each add.

• $Money

  Cost Per Use Calculator: What an Item Really Costs You

  Cost per use is the net cost of ownership -- price plus upkeep minus resale -- divided by an honest count of uses. The formula is simple; the usage estimate is where the comparison is won or lost.

• $Money

  Credit card payoff calculator: months to clear and interest paid

  A fixed payment behaves like an installment loan. A shrinking minimum payment does not. This page shows the arithmetic behind that difference and what it costs.

• $Money

  Inflation Calculator: What It Costs Later, What It's Worth Now

  One growth factor produces every output: future cost, present value, cumulative price change, buying power lost, and the years it takes prices to double.

• $Money

  Loan calculator: payment, total interest and the true APR

  The payment comes from one annuity formula. The real cost depends on the fee deducted before the money reaches you, which is what turns a quoted rate into an effective APR.

• $Money

  Mortgage payment calculator: what the monthly number is made of

  Price, down payment, rate and term set the principal and interest. Taxes, insurance, PMI and HOA set the rest. This page shows exactly how the payment is built.

• $Money

  Rent vs buy calculator: the answer depends on how long you stay

  Both households spend the same money each month, so the only question left is what each one holds at the end. This page shows the full calculation, step by step.

• $Money

  Savings Goal Calculator: How Long, and How Much a Month

  One annuity equation, solved three ways: time to reach a goal, the deposit needed to hit a deadline, and how much of the total the account actually contributes.

• $Money

  Tip Calculator: Pre-Tax vs Post-Tax, and Splitting the Bill

  Tipping on the total instead of the pre-tax amount adds exactly the tax times the tip rate. Here is the arithmetic, the mental shortcuts, and what rounding up really collects.

Salary conversions, take-home pay, overtime, freelance rates and paid leave.

• WWork & Pay

  Freelance hourly rate calculator: from take-home to price

  Start from the money you need to keep, gross up for self-employment tax, add expenses, and divide by the hours you can genuinely sell to find the rate that works.

• WWork & Pay

  Hourly to salary calculator: convert pay in both directions

  Turn an hourly rate into annual, monthly and per-paycheck pay, convert a salary back to an hourly rate, and see exactly what unpaid weeks off do to the comparison.

• WWork & Pay

  Overtime pay calculator: what a long week is actually worth

  Split a week into regular, overtime and double-time hours, price each correctly, and see the premium the overtime rule is really worth once bonuses join the regular rate.

• WWork & Pay

  PTO accrual calculator: hours, days and when the cap bites

  Turn an accrual rate into an annual allowance, project a balance twelve months out, and see how many pay periods it takes to reach a target before a cap stops the clock.

• WWork & Pay

  Real hourly wage calculator: pay divided by every hour

  Your nominal rate counts paid hours only. This works out pay after job costs divided by every hour the job takes, and shows why a bigger salary can be the worse deal.

• WWork & Pay

  Take-home pay calculator: what your paycheck is really worth

  See how gross salary becomes net pay: pre-tax deductions, 2026 federal brackets, Social Security up to the wage base, Medicare with its surtax, and a state rate you supply.

Ages, date differences and hours worked, calculated exactly.

• TTime & Dates

  Age calculator: exact age in years, months and days

  Calendar age is three subtractions with borrowing, not one division. Here is the algorithm, a worked example across a month boundary, and why decimal age differs.

• TTime & Dates

  Date difference calculator: days between two dates

  Two dates have more than one correct gap. This explains inclusive against exclusive counting, the weekday algorithm, and why months between dates is ambiguous.

• TTime & Dates

  Time card calculator: hours worked, breaks and overtime

  Payroll runs on decimal hours: 7:45 is 7.75, not 7.45. Here is the conversion, overnight shifts, paid against unpaid breaks, and why the week drives overtime.

Running costs, solar payback, paint quantities and room measurements.

• HHome & Energy

  Electricity cost calculator: what an appliance costs to run

  Watts are a rate, kilowatt-hours are what you buy. This shows the conversion step by step, how to find your effective rate, and why nameplate wattage misleads.

• HHome & Energy

  Paint calculator: how many gallons your room actually needs

  Wall area is exact arithmetic; coverage per gallon is a manufacturer's best case. This page separates the two so your paint estimate survives contact with a real wall.

• HHome & Energy

  Room area calculator: floor area, perimeter, wall area and volume

  Floor area, perimeter, wall area and volume from three measurements, in both unit systems, with the square-unit conversion error that ruins most flooring orders explained.

• HHome & Energy

  Solar payback calculator: breakeven years and cost per kWh

  Payback is not cost divided by savings once escalation and degradation are in play. Here is the accumulation, specific yield, levelized cost, and what is left out.

Fuel costs, economy conversions, EV comparisons and what a commute really costs.

• DDriving & Travel

  Commute Cost Calculator: What Getting to Work Really Costs

  Fuel is the visible cost and the smallest one. Here is how to build a real per-mile figure, price the hours, and turn a commute into a salary difference between two jobs.

• DDriving & Travel

  EV vs Gas Cost Calculator: What Each Car Costs Per Mile

  Put gasoline and electricity on the same footing: two cost-per-mile formulas, a worked annual comparison, and the charging and weather factors that move the answer.

• DDriving & Travel

  Fuel cost calculator: what a trip actually costs in fuel

  Distance, consumption and price give the trip cost. The annualized rows and the mpg illusion are where the arithmetic changes what you thought you knew.

• DDriving & Travel

  Fuel economy calculator: mpg, L/100 km, km/L and cost per mile

  One measurement, four incompatible units. This page shows how to measure economy properly, where the 235.215 conversion constant comes from, and what the number costs you.

BMI, daily energy needs and running pace, with the formulas shown.

• FHealth & Fitness

  BMI Calculator: How the Index Is Calculated and What It Shows

  BMI divides weight by height squared. This page derives the formula in both unit systems, works an example by hand, and sets out the limits of the index.

• FHealth & Fitness

  Calorie Calculator: How BMR and Daily Expenditure Are Estimated

  The Mifflin-St Jeor equation, written out and worked step by step, plus what BMR, RMR and TDEE each mean and how much error the activity multiplier introduces.

• FHealth & Fitness

  Running Pace Calculator: Pace, Splits and Race Predictions

  Pace is time divided by distance; a race prediction is a fitted curve. This page works both by hand and shows how far Riegel's formula can honestly be stretched.