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Calculators that show their working.
98 tools for money, health, maths, dates, conversions, study and building work. Every one prints its result on a tape with the numbers that produced it, so you can check the answer instead of trusting it.
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Finance 26
Loans, savings, tax and the arithmetic behind everyday money decisions.
401(k) calculatorProjects your 401(k) with employer match and salary growth — and flags match you are missing.
Amortization schedulePayment-by-payment table of principal, interest and balance — with the saving from overpaying.
Auto loan calculatorCar payment built from price, trade-in, tax and fees — the figures the dealer sheet actually contains.
Break-even calculatorUnits and revenue needed to cover your costs, plus the contribution margin behind the answer.
Compound interest calculatorGrowth on a starting balance plus regular deposits, with the interest split out from what you paid in.
Credit card payoff calculatorMonths and interest to clear a card balance — including what minimum payments actually cost.
Debt-to-income calculatorThe ratio underwriters check first — front-end and back-end, against the usual limits.
Discount calculatorSale price and savings from one or two stacked discounts, with tax added if you need it.
Emergency fund calculatorHow many months of essentials you actually hold, and how long the gap takes to close.
Home affordability calculatorHow much house your income supports, by the two ratios lenders actually apply.
Inflation calculatorWhat a price becomes after years of inflation, and what today’s money will actually buy.
Loan calculatorMonthly payment, total interest and the true cost of any amortising loan.
Mortgage calculatorFull monthly payment including tax, insurance, PMI and HOA — not just principal and interest.
Net worth calculatorEverything you own less everything you owe, with liquid net worth shown separately.
Overtime pay calculatorRegular and overtime hours priced separately, at any multiplier you like.
Take-home pay calculatorGross to net, per paycheck — with pre-tax and post-tax deductions kept separate.
Profit margin calculatorMargin and markup are not the same number — this shows both, and converts between them.
Refinance calculatorNew payment against old, and the month the closing costs finally pay for themselves.
Retirement calculatorProjects your balance at retirement and the yearly income it could sustainably support.
ROI calculatorTotal return and annualised return — the second is the one that lets you compare holdings fairly.
Salary calculatorConvert hourly, weekly, monthly and annual pay in either direction, including overtime.
Sales tax calculatorAdd tax to a price or strip it back out of a total — for sales tax, VAT or GST at any rate.
Savings goal calculatorThe monthly deposit needed to hit a target by a date, given what you already have saved.
Simple interest calculatorInterest that does not compound — plus a side-by-side comparison showing what compounding would add.
Student loan calculatorRepayment, total interest and the cost of interest accruing while you study.
Tip calculatorTip at any percentage, split between any number of people, with an option to round the total.
Health & fitness 16
Body composition, energy needs and training numbers, with their limits stated plainly.
BMI calculatorBody mass index in metric or imperial, with the categories and their limits explained.
BMR calculatorThe calories your body burns doing nothing at all, by the Mifflin-St Jeor equation.
Body fat calculatorBody fat percentage from tape measurements using the US Navy method, with lean mass split out.
Calorie calculatorDaily calorie needs from BMR and activity level, using Mifflin-St Jeor.
Calories burned calculatorEnergy cost of an activity from its MET value, your weight and the time you spent.
Pregnancy due date calculatorEstimated due date from LMP, conception or IVF transfer, with gestational age and trimester dates.
Ideal weight calculatorFour clinical formulas plus the healthy BMI range — shown as a range, because that is what it is.
Lean body mass calculatorLean mass and fat mass by the Boer, James and Hume formulas — or from a known body fat percentage.
Macro calculatorDaily calories and a protein/carb/fat split based on your activity level and goal.
One rep max calculatorEstimated 1RM from a submaximal set, by Epley and Brzycki, plus a training percentage table.
Ovulation calculatorEstimated fertile window and ovulation day from your cycle length, plus your next few periods.
Running pace calculatorPace, time or distance from any two — plus equivalent times for standard race distances.
Sleep calculatorBedtimes and wake times that land at the end of a cycle rather than the middle of one.
Target heart rate calculatorFive training zones from your age and resting heart rate, using the Karvonen method.
Waist-to-hip ratio calculatorWHR and waist-to-height, against WHO thresholds — where fat sits, not just how much.
Water intake calculatorDaily fluid target from weight, activity and climate — with food moisture counted separately.
Math 19
Arithmetic, algebra and statistics, with the working shown rather than hidden.
Average calculatorMean, median, mode, range and sum for any list of numbers, with the sorted data shown.
Circle calculatorGive any one of radius, diameter, area or circumference and get the other three.
Exponent and root calculatorPowers, nth roots and logarithms in any base — three views of the same relationship.
Factorial calculatorExact n! using big integers, with digit count and trailing zeros — not a rounded float.
Fraction calculatorAdd, subtract, multiply or divide fractions and mixed numbers, with the working shown.
GCF and LCM calculatorGCF and LCM for any list of whole numbers, with prime factorisations and Euclid’s steps.
Logarithm calculatorAny base, with log10, ln and log2 alongside and the change-of-base working shown.
Percentage calculatorPercent of a number, what percent one number is of another, and percentage change.
Permutation and combination calculatornPr and nCr, with and without repetition — and how to tell which one your problem needs.
Prime factorisation calculatorPrime factors, exponent form, every divisor and a primality check for any whole number.
Pythagorean theorem calculatorAny missing side of a right triangle, plus area, perimeter and both acute angles.
Quadratic equation solverRoots, discriminant, vertex and factored form for any ax² + bx + c = 0.
Random number generatorRandom whole numbers in any range, with or without repeats, using the browser’s secure generator.
Ratio calculatorSimplify ratios, solve A:B = C:? proportions, or divide a total into ratio parts.
Scientific calculatorTrig, logs, powers, roots, factorials and memory — with a running tape of everything you have entered.
Slope calculatorGradient between two points, plus the line equation, angle and distance.
Square root calculatorDecimal and exact surd form, plus nth roots and the perfect squares either side.
Standard deviation calculatorSample and population standard deviation, variance and standard error, with the working.
Z-score calculatorStandard score from mean and standard deviation, with percentile and tail probabilities.
Date & time 8
Durations, deadlines and timesheets, counted the way calendars actually behave.
Age calculatorExact age in years, months and days between any two dates.
Business days calculatorWorking days between two dates, or a deadline a set number of working days out.
Date calculator (add or subtract)Add or subtract days, weeks, months or years from a date — including working-days-only counting.
Days between dates calculatorCount days, weeks, months and working days between any two dates — with or without the end day.
Hours worked calculator (time card)A week of clock-in and clock-out times with breaks, overtime and gross pay.
Military time converter12-hour to 24-hour and back, including the midnight and noon cases people get wrong.
Time duration calculatorHours and minutes between two times, across midnight — plus decimal hours for timesheets.
Week number calculatorISO 8601 week number for a date, and the Monday-to-Sunday range any week covers.
Unit conversion 4
Metric, imperial and the places where the two quietly disagree.
Cooking measurement converterCups to grams for real ingredients, plus spoons, ounces, millilitres and oven temperatures.
Roman numeral converterBoth directions, with strict validation — it rejects IIII and IC rather than guessing.
Shoe size converterUS, UK, EU and CM from a measured foot length — the only input that means anything.
Unit converterLength, weight, temperature, area, volume, speed, pressure, energy, data and time — metric and imperial.
Education 5
Grades, averages and what you need on the paper that is left.
Final grade calculatorThe score you need on the final to hit your target grade — and whether it is reachable.
GPA calculatorSemester and cumulative GPA on the 4.0 scale, weighted or unweighted, with credit hours.
Grade calculator (weighted)Your overall course grade from weighted categories — and which one is really moving it.
Reading time calculatorWord count to minutes, for silent reading, speaking aloud and audiobook narration.
Test score calculatorMarks to percentage and letter grade, plus how many you can afford to miss.
Home & construction 9
Areas, volumes and material quantities for jobs around the house.
BTU calculatorRoom heating and cooling load in BTU and kW, adjusted for insulation, sun and occupancy.
Concrete calculatorCubic yards, cubic metres and bag counts for slabs, footings, columns and post holes.
Drywall calculatorSheets, screws, tape and compound for a room, with openings deducted and waste added.
Gravel and mulch calculatorVolume, weight and bag counts for gravel, mulch, sand, topsoil and bark at any depth.
Paint calculatorLitres or gallons for a room, allowing for doors, windows, coats and real spread rates.
Roofing calculatorTrue roof area from footprint and pitch — the slope multiplier most estimates forget.
Square footage calculatorArea for rectangles, L-shapes, circles and triangles — in feet or metres, with cost per unit.
Stair calculatorRise, going, stringer length and total run — checked against the usual comfort rules.
Tile calculatorTile counts, boxes, waste and estimates for adhesive and grout — floors or walls.
Auto & travel 4
Fuel, distance and what a journey actually costs.
EV charging cost calculatorCost per charge, cost per mile and charging time — plus the petrol comparison.
Fuel cost calculatorWhat a journey costs in fuel — MPG or L/100 km, one way or return, split between passengers.
Gas mileage calculator (MPG)Your real MPG from odometer readings and fuel added — not the sticker figure.
Tire size calculatorCompare two tyre sizes for diameter and circumference, with the speedometer error.
Tech & everyday 7
Networks, number bases and a few things that did not fit anywhere else.
Aspect ratio calculatorMissing width or height at a fixed ratio, and the simplified ratio of any resolution.
Colour converterHEX, RGB, HSL and CMYK from any one of them, with luminance for contrast work.
Download time calculatorTransfer time from size and speed, with the bits-versus-bytes factor of eight handled.
Hex, binary and decimal converterBinary, octal, decimal, hex and any base from 2 to 36 — with bit patterns and two’s complement.
Password strength calculatorEntropy in bits, estimated crack time, and why length beats complexity every time.
Subnet calculator (IPv4)Network, broadcast, host range, wildcard mask and host count from any IPv4 address and prefix.
Uptime and SLA calculatorWhat each "nine" actually buys you in allowed downtime, per day, month and year.
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