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Calculator guides for real money, math, health, date, and conversion questions.

Read practical explainers that show the formula, inputs, assumptions, common mistakes, and related tools behind each calculator. Start with a featured guide or browse the full library by topic.

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Mortgage Calculator topic photoFinanceHow to Calculate a Mortgage Payment by HandWork out a monthly mortgage payment step by step: the amortization formula, adding taxes and insurance, and the mistakes that throw estimates off.Practical guide · Mortgage Calculator
Loan Calculator topic photoFinanceHow to Calculate Loan Payments: Formula, Fees and PayoffLearn how loan payments are calculated, why early payments are mostly interest, and how fees, term length and extra payments change what a loan costs.Practical guide · Loan CalculatorCar Loan Calculator topic photoFinanceHow to Calculate a Car Payment From Sticker Price to Monthly BillWork out a car payment step by step: out-the-door price, trade-in equity, amount financed and the loan formula, with the mistakes that cost buyers money.Practical guide · Car Loan CalculatorPersonal Loan Calculator topic photoFinanceHow Personal Loan Interest Works, Month by MonthSee how personal loan interest is charged each month, why the fee matters as much as the rate, and how term length and extra payments change the total cost.Practical guide · Personal Loan CalculatorBusiness Loan Calculator topic photoFinanceHow to Calculate Business Loan Payments and Test AffordabilityLearn how business loan payments are calculated, how fees and interest-only periods change them, and how to check the payment against your cash flow.Practical guide · Business Loan Calculator

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Home Equity Loan Calculator topic photoFinanceHow Much Home Equity Can You Borrow? CLTV ExplainedFind out how lenders decide how much equity you can borrow, how CLTV limits work, and what appraisals, existing liens and closing costs do to your number.Practical guide · Home Equity Loan CalculatorCompound Interest Calculator topic photoFinanceThe Compound Interest Formula Explained Step by StepWhat each part of A = P(1 + r/n)^(nt) means, how to work it by hand, how to add monthly deposits, and the mistakes that throw the answer off.Practical guide · Compound Interest CalculatorInvestment Calculator topic photoFinanceHow Much Will My Investment Grow? The Three Things That Decide ItSee how time, monthly contributions and return shape investment growth, with worked numbers for a lump sum, monthly investing and the cost of a late start.Practical guide · Investment CalculatorSavings Calculator topic photoFinanceHow Long Will It Take to Save for Your Goal?Work out how many months it takes to reach a savings goal, see how bigger deposits and APY change the date, and avoid the mistakes that stretch the timeline.Practical guide · Savings CalculatorRetirement Calculator topic photoFinanceHow Much Do You Need to Retire? Find Your Number in Four StepsWork out your retirement number from spending, outside income, inflation and a withdrawal rate, with a worked example and the mistakes that skew the answer.Practical guide · Retirement CalculatorAnnuity Calculator topic photoFinanceThe Future Value of an Annuity Formula, With Worked ExamplesHow the future value of an annuity formula works, how to solve it by hand for ordinary annuities and annuities due, and the slips that give wrong answers.Practical guide · Annuity CalculatorCredit Card Payoff Calculator topic photoFinanceHow Long Does It Take to Pay Off a Credit Card?How long it takes to pay off a credit card at different payments, why small payments drag on for years, and three ways to get to zero sooner.Practical guide · Credit Card Payoff CalculatorDebt Payoff Calculator topic photoFinanceDebt Snowball vs Avalanche: Which Payoff Method Should You Use?How the debt snowball and avalanche methods work, when the avalanche saves real money, when the snowball's quick wins are worth it, and how to choose.Practical guide · Debt Payoff CalculatorAmortization Calculator topic photoFinanceHow Loan Amortization Works, Payment by PaymentA plain walk-through of loan amortization: how each payment splits between interest and principal, why long loans start slow, and how extra payments help.Practical guide · Amortization CalculatorMortgage Extra Payment Calculator topic photoFinanceIs Paying Extra on Your Mortgage Worth It?When paying extra on your mortgage makes sense, when it doesn't, how much it saves, and what to check before you send money to your servicer.Practical guide · Mortgage Extra Payment CalculatorVAT Calculator topic photoBusinessHow to Calculate VAT: Add It, Remove It and Check ItHow to calculate VAT by hand: add it to a net price, remove it from a gross price, spot the 20% mistake and check your answer, with worked examples.Practical guide · VAT CalculatorMargin Calculator topic photoBusinessHow to Calculate Profit Margin: Gross, Operating and NetHow to calculate profit margin step by step, the difference between gross, operating and net margin, and the mistakes that make margins look better than they are.Practical guide · Margin CalculatorMarkup Calculator topic photoBusinessMarkup vs Margin: The Difference and How to ConvertMarkup vs margin explained with simple examples, conversion formulas both ways, a quick chart, and the pricing mistakes that come from mixing them up.Practical guide · Markup CalculatorProfit Calculator topic photoBusinessHow to Calculate Profit: A Plain Guide for Small BusinessesHow to calculate profit for a small business or side hustle, with worked examples, the costs people forget and the reasons profit and cash don't match.Practical guide · Profit CalculatorTip Calculator topic photoBusinessHow Much to Tip: Restaurants, Delivery, Salons and MoreHow much to tip at restaurants, bars, for delivery, haircuts, taxis and hotels in the US, what most Americans tip, and when a service charge changes things.Practical guide · Tip CalculatorYouTube Revenue Calculator topic photoBusinessHow Much Does YouTube Pay per 1,000 Views?What YouTube pays per 1,000 views, why there's no single rate, how RPM and CPM differ, what creators keep from ads and Shorts, and how to estimate your own.Practical guide · YouTube Revenue CalculatorSalary to Hourly Calculator topic photoBusinessHow to Convert Salary to Hourly Pay (and Which Hours to Count)A plain guide to turning a yearly salary into an hourly rate: the 2,080-hour method, when to use other hours, and the mistakes that skew job comparisons.Practical guide · Salary to Hourly CalculatorHourly to Salary Calculator topic photoBusinessHow to Convert Hourly Pay to a Yearly SalaryTurn an hourly wage into annual pay the right way: the 2,080-hour method, quick mental math, and how part-time hours, time off and overtime change the answer.Practical guide · Hourly to Salary CalculatorPercentage Calculator topic photoMathHow to Calculate Percentages Without Getting the Base WrongEvery percent problem is part, whole and rate. Learn the three core formulas, percent change, reverse percentages, mental math shortcuts and the usual traps.Practical guide · Percentage CalculatorFraction Calculator topic photoMathHow to Add, Subtract, Multiply and Divide FractionsThe four fraction rules in plain terms, why adding needs a common denominator and multiplying doesn't, how to handle mixed numbers, and the mistakes to avoid.Practical guide · Fraction CalculatorDecimal to Fraction Calculator topic photoMathHow to Convert a Decimal to a Fraction, Step by StepThree methods for turning decimals into fractions: decimals that end, decimals that repeat, and repeats with a delay. Worked examples and common mistakes.Practical guide · Decimal to Fraction CalculatorRatio Calculator topic photoMathHow to Simplify and Scale Ratios, With Worked ExamplesSimplify any ratio with one common factor, clear decimals and fractions, then scale it up or down. Worked examples from recipes, screens and budgets.Practical guide · Ratio CalculatorProportion Calculator topic photoMathHow to Solve a Proportion, From Setup to AnswerLearn to set up and solve proportions with cross multiplication, avoid the setup mistakes that cause most wrong answers, and spot when a problem isn't proportional.Practical guide · Proportion CalculatorLCM Calculator topic photoMathHow to Find the Least Common Multiple: 3 Methods ComparedThree ways to find the least common multiple, when each one is fastest, worked examples for two and three numbers, and the mistakes that trip people up.Practical guide · LCM CalculatorGCF Calculator topic photoMathHow to Find the Greatest Common Factor (With Examples)Three ways to find the greatest common factor, worked examples for two and three numbers, when to use each method, and the slips that lead to wrong answers.Practical guide · GCF CalculatorSlope Calculator topic photoMathHow to Find Slope From Two Points (Step by Step)Find the slope between two points in four steps, with examples using negatives and fractions, plus the mistakes that flip the sign or break the answer.Practical guide · Slope CalculatorQuadratic Formula Calculator topic photoMathHow to Use the Quadratic Formula: Steps, Examples and MistakesA step-by-step guide to the quadratic formula with three worked examples, how to simplify the square root, and the sign mistakes that cause wrong answers.Practical guide · Quadratic Formula CalculatorFactoring Calculator topic photoMathHow to Factor Trinomials: The AC Method and ShortcutsFactor trinomials when a = 1 and when a is bigger, using the sum and product trick and the AC method, with worked examples and the sign rules that help.Practical guide · Factoring CalculatorScientific Calculator topic photoMathHow to Use a Scientific Calculator: The Keys That Trip People UpA practical guide to using a scientific calculator: order of operations, negative numbers, degree and radian mode, EXP versus ^, log versus ln, and Ans.Practical guide · Scientific CalculatorGPA Calculator topic photoStudentsHow to Calculate GPA: Step by Step, With ExamplesLearn how to calculate GPA by hand: convert grades to points, weight them by credits, combine terms into a cumulative GPA, and avoid the usual mistakes.Practical guide · GPA CalculatorBMI Calculator topic photoHealthWhat Is a Healthy BMI? Ranges, Limits and What to Check NextA healthy BMI for adults is 18.5 to under 25. Here's where that range comes from, who it fits poorly, and what else is worth checking beyond BMI.Practical guide · BMI CalculatorTDEE Calculator topic photoHealthWhat Is TDEE? Total Daily Energy Expenditure, ExplainedTDEE is the total energy you burn in a day. Learn what goes into it, how calculators estimate it, why estimates miss, and how to find your real number.Practical guide · TDEE CalculatorBMR Calculator topic photoHealthBMR vs TDEE: What Each Number Means and Which to UseBMR is what you burn at rest. TDEE is what you burn in a full day. Here's how they connect, worked examples for both, and which one to plan your calories on.Practical guide · BMR CalculatorCalorie Deficit Calculator topic photoHealthHow Big Should a Calorie Deficit Be? Sizing It for Your BodyHow big a calorie deficit should be: what guidelines say, why a percentage of TDEE often works better than a fixed number, and the warning signs it's too big.Practical guide · Calorie Deficit CalculatorIdeal Weight Calculator topic photoHealthIdeal Weight Formulas Compared: Devine, Robinson, Miller and HamwiDevine, Robinson, Miller and Hamwi side by side: where each formula came from, how far apart they land at different heights, and which to use when.Practical guide · Ideal Weight CalculatorAge Calculator topic photoDate & TimeHow to Calculate Age From Date of Birth (Step by Step)Work out anyone's age from their date of birth by hand: whole years, then months and days, with worked examples, leap-day rules and an Excel formula.Practical guide · Age CalculatorAge Difference Calculator topic photoDate & TimeHalf Your Age Plus Seven: How the Age Gap Rule WorksWhat the half-your-age-plus-seven rule says, where it came from, what research found, and how to work out the rule for any age.Practical guide · Age Difference CalculatorDate Calculator topic photoDate & TimeHow to Add or Subtract Days From a Date Without MistakesCount forward or back from any date by hand: the month-by-month method, the 30-versus-31 trap, weeks, month ends and the spreadsheet formulas that do it.Practical guide · Date CalculatorDays Between Dates Calculator topic photoDate & TimeHow to Count Days Between Two Dates by HandThree ways to count the days between two dates by hand, when to add one for the end date, how to check your answer and the spreadsheet formula that does it.Practical guide · Days Between Dates CalculatorNext Birthday Calculator topic photoDate & TimeHow Many Days Until My Birthday? How to Count It YourselfCount the days to your next birthday by hand, check the answer with weeks, find the weekday it falls on and avoid the classic off-by-one slip.Practical guide · Next Birthday CalculatorSchool Age Calculator topic photoDate & TimeWhat Grade Should My Child Be In? Age-by-Grade GuideA U.S. age-by-grade chart, how kindergarten cutoff dates decide the starting year, how to work out any year's grade and when a child may not follow the chart.Practical guide · School Age CalculatorLife Stats Calculator topic photoDate & TimeHow Many Days Have I Been Alive? Three Ways to Work It OutWork out how many days you've been alive with a quick shortcut, a spreadsheet formula or a calendar count, and find your 10,000-day birthday.Practical guide · Life Stats CalculatorZodiac Sign Calculator topic photoDate & TimeZodiac Sign Dates: All 12 Signs by MonthEvery zodiac sign's start and end date, a month-by-month list, why some charts differ by a day, and what to do if your birthday falls on a cusp.Practical guide · Zodiac Sign CalculatorBusiness Days Calculator topic photoDate & TimeHow to Count Business Days Between Two DatesCount business days by hand or in a spreadsheet: the weekday shortcut, start and end date rules, weekend holidays, and the mistakes that throw deadlines off.Practical guide · Business Days CalculatorWork Hours Calculator topic photoDate & TimeHow to Calculate Hours Worked From a Time CardA step-by-step way to total hours worked from clock-in and clock-out times, handle breaks and overnight shifts, and convert minutes to decimal for payroll.Practical guide · Work Hours CalculatorUnit Converter topic photoConvertersMetric and Imperial Units Explained, With Exact ConversionsHow the metric and imperial systems are built, why U.S. and British units differ, the exact factors that link them, and the conversion mistakes to avoid.Practical guide · Unit ConverterNumbers to Words Converter topic photoConvertersHow to Write Numbers in Words: Rules, Styles and ExamplesWhen to spell numbers out, how hyphens and "and" work, and how AP and Chicago style differ, with examples for big numbers, decimals and checks.Practical guide · Numbers to Words ConverterVolume Calculator topic photoConvertersVolume Formulas for Common Shapes, and Why They WorkThe volume formulas for boxes, cylinders, cones, pyramids and spheres, how they connect to each other, and the measuring mistakes that throw answers off.Practical guide · Volume CalculatorSteps to Miles Calculator topic photoConvertersHow Many Steps Are in a Mile? What Changes the NumberWhy a mile takes some people 2,000 steps and others 2,500, how height, pace and running change it, and how to find your own steps per mile.Practical guide · Steps to Miles CalculatorSquare Footage Calculator topic photoConvertersHow to Calculate Square Footage of a Room or HouseA step-by-step way to measure and calculate square footage for rooms, odd shapes and whole floors, with worked examples and the mistakes that cost you money.Practical guide · Square Footage CalculatorFuel Cost Calculator topic photoConvertersHow to Calculate Gas Cost for a Trip (and Get Close to the Real Bill)The three-step formula for trip gas cost, how to find your real MPG, what changes it on the road, and the mistakes that make estimates miss.Practical guide · Fuel Cost CalculatorGrade Calculator topic photoStudentsWhat Do I Need on My Final Exam? How to Work It OutWork out the score you need on your final exam for the grade you want, with the formula, worked examples and the mistakes that throw the answer off.Practical guide · Grade CalculatorLove Calculator topic photoEverydayHow Love Calculators Work (and Why They're Just for Fun)The letter-counting trick behind classic love tests, how online love calculators turn names into percentages, and why people still believe the results.Practical guide · Love CalculatorHours Calculator topic photoDate & TimeHow to Add Hours and Minutes Without MistakesAdd and subtract hours and minutes by hand: carrying 60 minutes, converting to decimal, adding time to a clock time, and the slips that throw totals off.Practical guide · Hours CalculatorDice Roller topic photoEverydayDice Probability Explained: Odds for 1, 2 and 3 DiceHow to work out dice odds by counting outcomes, why 7 is the most common roll with two dice, how 3d6 forms a bell curve, and what rolling twice does to a d20.Practical guide · Dice RollerSpeed Calculator topic photoConvertersThe Speed, Distance and Time Formula, With ExamplesHow the speed distance time formula works, the triangle trick, unit conversions, and the mistakes that trip up students and drivers, with worked answers.Practical guide · Speed CalculatorMass Calculator topic photoConvertersMass vs Weight: What's the Difference and Why It MattersMass is how much matter you have; weight is the pull of gravity on it. See the formula, worked examples on Earth and the Moon, and why scales show kg.Practical guide · Mass CalculatorSleep Calculator topic photoHealthHow Sleep Cycles Work: Stages, Timing and the 90-Minute MythWhat happens in each stage of a sleep cycle, why cycles run 80 to 100 minutes, how the night shifts from deep sleep to REM, and what it means for your alarm.Practical guide · Sleep CalculatorShoe Size Conversion Calculator topic photoConvertersHow Shoe Size Systems Differ: US, UK, EU and MondopointWhy a US 9 isn't a UK 9, where EU sizes and Mondopoint come from, why women's and men's sizes don't line up, and how to convert sizes without guessing.Practical guide · Shoe Size Conversion CalculatorRandom Number Generator topic photoEverydayHow Random Number Generators Work: PRNG, CSPRNG and True RandomnessWhat separates pseudo-random, cryptographically secure and true random number generators, how browsers make random numbers, and the bias mistake to avoid.Practical guide · Random Number GeneratorBinary Calculator topic photoMathHow Binary Addition and Subtraction WorkBinary addition and subtraction explained with carries, borrows and two's complement, plus worked examples and the slips that trip up most students.Practical guide · Binary CalculatorPregnancy Calculator topic photoHealthHow Pregnancy Weeks Are Counted (and Why It Starts Before Conception)Why pregnancy weeks start at your last period, what 14 weeks 1 day means, how weeks map to trimesters and months, and why your due date may change.Practical guide · Pregnancy CalculatorMacro Calculator topic photoHealthHow to Calculate Macros by Hand in Four StepsWork out your protein, carb and fat grams yourself: set calories, anchor protein, pick a fat share, fill in carbs. With examples and common mistakes.Practical guide · Macro CalculatorProtein Calculator topic photoHealthHow Much Protein Do You Need Per Day? Picking the Right NumberWhy protein advice ranges from 0.8 to 2.0 g/kg, which number fits your situation, and how to turn it into grams you can actually eat.Practical guide · Protein CalculatorAPR Calculator topic photoFinanceAPR vs Interest Rate: What Each One Tells YouAPR vs interest rate explained with real loan numbers: why APR runs higher, when a lower APR still costs more, and how to compare offers properly.Practical guide · APR CalculatorBudget Calculator topic photoFinanceThe 50/30/20 Budget Rule: How It Works and When to Bend ItWhat the 50/30/20 budget rule says, how to apply it to your take-home pay, what counts as a need, and how to adjust the split when your rent is high.Practical guide · Budget CalculatorIRR Calculator topic photoFinanceHow to Calculate IRR: By Hand, in Excel and When Not to Trust ItLearn how to calculate IRR step by step with trial and error, see the Excel function, and learn the three situations where IRR gives a misleading answer.Practical guide · IRR CalculatorIRA Calculator topic photoFinanceTraditional IRA vs Roth IRA: Which One Leaves You More?Traditional or Roth IRA? See why the answer comes down to your tax rate now versus later, with a worked example, 2026 income rules and withdrawal rules.Practical guide · IRA CalculatorDiscount Calculator topic photoBusinessHow to Calculate a Discount: Sale Prices, Percent Off and Stacked DealsHow to calculate a discount by hand: sale price, amount saved, percent off between two prices, original price, stacked deals and coupons, with quick mental tricks.Practical guide · Discount CalculatorBond Calculator topic photoFinanceHow Bond Prices and Yields Work, With Worked NumbersWhy bond prices fall when yields rise, how coupon rate, current yield and YTM differ, and why long bonds swing more. Every point uses real numbers.Practical guide · Bond CalculatorRoth IRA Calculator topic photoFinanceHow Much Will My Roth IRA Be Worth? What Moves the NumberSee what a Roth IRA could be worth at retirement, why starting age matters more than return, and how fees and inflation shrink the final number.Practical guide · Roth IRA CalculatorIncome Tax Calculator topic photoFinanceHow Federal Tax Brackets Work, With 2026 ExamplesWhy moving into a higher tax bracket never taxes all your income at the new rate, how to work out tax slice by slice, and what marginal rates mean for you.Practical guide · Income Tax CalculatorSalary Calculator topic photoBusinessHow to Calculate a Raise: Percent, Dollars and Take-Home PayWork out a raise as a percentage or a dollar amount, find the percent increase between two salaries, and see how much of a raise reaches your paycheck.Practical guide · Salary CalculatorInterest Rate Calculator topic photoFinanceHow to Find the Interest Rate on a LoanThree ways to find the interest rate on a loan: from your documents, from your payment, or from your statement. Includes worked numbers and common mistakes.Practical guide · Interest Rate CalculatorHouse Affordability Calculator topic photoFinanceHow Much House Can I Afford? A Realistic Way to Set Your BudgetHow much house you can afford on your income, why the lender's number isn't your budget, and the costs and cash checks first-time buyers often miss.Practical guide · House Affordability CalculatorRent Calculator topic photoFinanceHow Much Rent Can I Afford? Rules of Thumb and a Better BudgetHow much rent you can afford using the 30% rule, the 3x income rule and a real take-home budget, with examples by income and the costs renters often forget.Practical guide · Rent CalculatorAnnuity Payout Calculator topic photoFinanceHow Annuity Payouts Are Calculated (and Why Quotes Differ)The math behind annuity payouts, what an insurer adds for lifetime income, and how term, return, fees, timing and rising payments change your monthly check.Practical guide · Annuity Payout CalculatorPension Calculator topic photoFinancePension Lump Sum vs Monthly Payments: How to Compare ThemHow to compare a pension lump sum with monthly payments: present value, break-even age, survivor needs, inflation and risk, with worked numbers.Practical guide · Pension CalculatorRefinance Calculator topic photoFinanceWhen Does Refinancing Make Sense? A Practical TestA clear way to decide if refinancing your mortgage makes sense: break-even, how long you'll stay, term choice, points and the traps that erase savings.Practical guide · Refinance CalculatorAuto Lease Calculator topic photoFinanceHow Car Lease Payments Are Calculated, Step by StepHow car lease payments are calculated: cap cost, residual, depreciation, money factor and tax, with a worked example and what moves the payment most.Practical guide · Auto Lease CalculatorWord Counter topic photoTextHow Many Words Is a Page? Single vs Double SpacedHow many words fit on a page single or double spaced, why the number changes with font and layout, and how to convert a word limit into pages.Practical guide · Word CounterCharacter Counter topic photoTextCharacter Limits for Social Media: Posts, Captions and TitlesCurrent character limits for X, Threads, Instagram, YouTube, Google Ads and SMS, how each one counts emoji and links, and how to write to fit them.Practical guide · Character Counter