Free calculators, grouped by what you need

Countdown to any future date — birthdays, holidays, deadlines.

Add or subtract days, weeks, months, years, or business days from any date.

Days, weeks, months, and years between any two dates — with optional business-days-only count.

Count business days between two dates or add/subtract working days from any date, with custom holidays excluded.

Add up hours worked between start and end times, minus breaks.

Convert any date and time between time zones — DST aware.

Count business days between two dates or add/subtract working days from any date, with custom holidays excluded.

Drift-free stopwatch with laps and a countdown timer with audible alert — millisecond accuracy.

Your exact age in years, months, days, hours, and minutes.

Countdown to any future date — birthdays, holidays, deadlines.

Monthly payment, taxes, insurance, and required income.

Monthly savings, break-even point, and lifetime savings from refinancing.

Compare the true 5-year cost of renting versus buying.

Home equity line of credit: max borrow, interest-only payment, and full repayment cost.

Monthly payment and total interest for any personal or auto loan.

Monthly car payment including tax, trade-in, and down payment.

How long it takes — and how much interest you'll pay — at your current monthly payment.

Home equity line of credit: max borrow, interest-only payment, and full repayment cost.

Project your retirement balance with employer match and growth.

Project your investment growth over years or decades.

Total return, profit, and annualized CAGR for any investment.

Convert between APR and APY for any compounding frequency.

Estimate take-home pay after federal, state, and FICA taxes.

Annual and biweekly net pay after federal, FICA, and state income tax — all 50 states plus DC.

Convert hourly wage to annual salary (and back) with custom hours per week.

Estimate 1099 SE tax, federal and state income tax, and quarterly payments.

Calculate tips and split the bill between any number of people.

Find the sale price after any percentage discount.

Add sales tax, GST, HST, or VAT to any price and see the final total.

What a dollar from any year is worth today — adjust for the inflation rate.

Live exchange rates between major world currencies — updated daily (ECB).

Salary you need in another city to maintain the same standard of living.

How much to save monthly to hit any goal by a target date.

Add up assets, subtract liabilities, see your total net worth.

Project your investment growth over years or decades.

Capitalization rate from NOI and value, or solve for value, NOI, or required cap rate.

Annual cash flow divided by cash invested — the levered return on a rental property.

Gross and net rental yield from purchase price, monthly rent, expenses, and vacancy.

Apartment building NOI, cap-rate value, value per door, and DSCR.

Pick a property type — multifamily, hotel, retail, office, or industrial — and underwrite it.

Apartment building NOI, cap-rate value, value per door, and DSCR.

ADR × Occupancy × Keys → RevPAR, NOI, and value per key.

Strip center / NNN proforma: rent PSF, CAM recovery, NOI, value per SF.

Office building NOI, rent PSF, expense recoveries, and value per SF.

Warehouse / distribution NOI, NNN rent PSF, and value per SF.

Underwrite a self-storage facility: NRSF, GPI, vacancy, NOI, cap-rate value, and value per square foot and per unit.

Maximum offer for a flip — 70% of ARV minus repairs, with adjustable spread for any market.

Deferred gain, recognized boot from cash and debt relief, federal tax owed, and carryover basis on a like-kind real estate exchange.

Buyer closing-cost breakdown by line item — lender, title, government, prepaids — plus cash-to-close.

Body mass index in metric or US units, with category.

Estimate body fat percent with the US Navy circumference method, plus a BMI-based check.

Models the body as an ellipse from waist and height — predicts mortality risk better than BMI.

Keep your waist under half your height — the simple cardiometabolic risk screen.

Estimate ideal body weight from height, sex, and frame using Hamwi, Devine, Robinson, and Miller formulas, plus the healthy-BMI range.

Daily calories to lose, maintain, or gain weight using Mifflin-St Jeor.

Daily calorie target for weight loss at your chosen pace, plus weeks to your goal — companion to the TDEE calculator.

Basal metabolic rate using Mifflin-St Jeor and Harris-Benedict, with activity-multiplier TDEE.

Daily protein, carbs, and fat targets for cutting, maintenance, or bulking based on your TDEE.

How many ounces, cups, or liters you should drink each day.

Pace per mile/km and average speed from time and distance.

Estimate your 1RM from a working set using Epley, Brzycki, Lombardi, O'Conner, and Lander formulas.

Calculate your five training heart-rate zones from age and resting HR using Tanaka, Fox, Gulati, or Karvonen heart-rate-reserve formulas.

Estimated ovulation date, six-day fertile window, and next expected period from your last menstrual period and cycle length.

Estimate your due date and current week of pregnancy.

Convert your dog's age to human years using the AVMA size-aware method or the 2019 epigenetic clock, with small/medium/large/giant adjustments.

Best bedtime or wake time based on 90-minute sleep cycles.

How many ounces, cups, or liters you should drink each day.

Calculate your semester or cumulative GPA on a 4.0 scale.

Find the GPA you need on remaining coursework to hit a target cumulative GPA.

Weighted course grade from assignments, quizzes, and exams. Shows current grade plus the score needed on remaining work.

Three modes: X% of Y, A is what % of B, and % change.

Percent change between any old and new value, with the formula and direction shown.

Mean, median, mode, sum, count, min, max, and range for any list of numbers.

Solve any proportion a/b = c/d for the missing value using cross-multiplication.

Convert rise and run into decimal slope, percent grade, angle, and 1:N ratio — for ramps, roofs, roads, stairs.

Add, subtract, multiply, and divide fractions and mixed numbers — results returned simplified, as a mixed number, and as a decimal.

Mean, median, mode, range, sample/population standard deviation, variance, quartiles, IQR, and SEM for any list of numbers.

Free online scientific calculator with trig, logs, exponents, square roots, parentheses, and constants pi and e.

Find the area of a circle from its radius, diameter, or circumference with the exact formula A = π × r².

Find the circumference of a circle from its radius, diameter, or area using C = 2 × π × r.

Volume and surface area of any cylinder from its radius and height using V = π × r² × h.

Volume and surface area of a sphere from its radius or diameter — uses V = (4/3) × π × r³.

Volume, slant height, and surface area of a cone from base radius and height using V = (1/3) × π × r² × h.

Volume, surface area, and diagonal of a rectangular box from length, width, and height (V = L × W × H).

Convert a value to a z-score, percentile, and tail probabilities using the standard normal distribution.

Find P(X<x), P(X>x), and between-range probabilities for any normal distribution with mean μ and SD σ.

Compute P(X=k), cumulative probabilities, mean, and variance for n trials with success probability p.

Model rare events with rate λ — get P(X=k), cumulative probability, mean, and variance.

Compute nPr (order matters) and nCr (order doesn't) with full counting-principle explanation.

Update prior beliefs with new evidence using Bayes' rule — posterior probability with tree diagram.

Compute z or t confidence intervals for a mean, with margin of error breakdown.

One-sample and two-sample t-tests with t-statistic, p-value, and rejection regions.

Goodness-of-fit and independence tests with expected counts, chi-square statistic, and p-value.

Pearson correlation coefficient r with scatter plot, regression line, and interpretation guide.

Least-squares slope, intercept, R², and predictions for any paired (x, y) data.

Required sample size to estimate a proportion or mean at a chosen confidence level and margin of error.

Length, weight, and volume between metric and imperial.

Convert between m² and ft² — plus square yards, acres, and hectares.

Convert inches to centimeters using the exact international factor (1 in = 2.54 cm) — plus mm, m, and feet.

Convert shoe sizes between US (men's & women's), UK, European, Japanese (cm), and foot length in centimetres.

Cups, tablespoons, grams, ounces, and milliliters — plus oven temperature conversions.

Convert between Fahrenheit, Celsius, and Kelvin instantly in either direction.

Convert milliliters to fluid ounces — covers both US (29.57 ml) and UK Imperial (28.41 ml) fluid ounces.

Convert fluid ounces to cups (US and UK), with tablespoons and milliliters.

MPG from miles and gallons, plus total trip fuel cost at any price per gallon.

Convert between Arabic numbers and Roman numerals — both directions, 1 to 3999, with validation.

Gallons of paint needed for a room or surface — adjusts for doors, windows, coats, and ceiling.

Rolls needed including pattern-repeat waste, doors, and windows.

Tiles and boxes needed with grout joint width and waste buffer.

Cubic yards needed for slabs, driveways, and patios — plus bags and cost.

Calculate board feet for dimensional lumber. Add multiple sizes for total board feet, lineal feet, waste, and cost.

Cubic yards, cubic feet, bags, and tons of mulch, gravel, topsoil, or sand to cover a rectangular area at any depth.

Area in sq ft, m², and sq yd with waste factor and material cost.

Annual kWh production, first-year electric-bill savings, simple payback in years, and 25-year savings from rooftop solar.