Ten Key Calculators

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Ten Key Calculators Suite body { font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; line-height: 1.6; margin: 0; padding: 20px; background-color: #f8f9fa; color: #333; } .loan-calc-container { max-width: 800px; margin: 30px auto; padding: 25px; background-color: #ffffff; border-radius: 8px; box-shadow: 0 4px 15px rgba(0, 0, 0, 0.05); border: 1px solid #e0e0e0; } h1, h2 { color: #004a99; text-align: center; margin-bottom: 20px; } .calculator-section { margin-bottom: 30px; padding: 20px; border: 1px solid #e0e0e0; border-radius: 5px; background-color: #fdfdfd; } .input-group { margin-bottom: 15px; display: flex; flex-wrap: wrap; align-items: center; } .input-group label { flex: 1 1 150px; /* Grow, shrink, basis */ min-width: 120px; margin-right: 15px; font-weight: 500; color: #004a99; } .input-group input[type="number"], .input-group input[type="text"] { flex: 2 2 200px; /* Grow, shrink, basis */ padding: 10px 12px; border: 1px solid #ccc; border-radius: 4px; font-size: 1rem; box-sizing: border-box; } .input-group input[type="number"]:focus, .input-group input[type="text"]:focus { border-color: #007bff; outline: none; box-shadow: 0 0 0 2px rgba(0,123,255,.25); } button { display: block; width: 100%; padding: 12px 20px; background-color: #004a99; color: white; border: none; border-radius: 5px; font-size: 1.1rem; cursor: pointer; transition: background-color 0.3s ease; margin-top: 20px; } button:hover { background-color: #003366; } .result-section { margin-top: 30px; padding: 20px; background-color: #e7f3ff; border-left: 5px solid #004a99; border-radius: 5px; } .result-section h3 { color: #004a99; margin-top: 0; } #result { font-size: 1.8rem; font-weight: bold; color: #28a745; text-align: center; } .article-content { margin-top: 40px; padding: 20px; background-color: #ffffff; border: 1px solid #e0e0e0; border-radius: 8px; } .article-content h2 { text-align: left; color: #004a99; } .article-content p, .article-content ul { margin-bottom: 15px; } .article-content strong { color: #004a99; } .calculator-selection { text-align: center; margin-bottom: 30px; } .calculator-selection select { padding: 10px 15px; border: 1px solid #ccc; border-radius: 4px; font-size: 1rem; min-width: 250px; } /* Hide all calculators by default */ .calculator-form { display: none; } /* Show the active calculator */ .calculator-form.active { display: block; }

Ten Key Calculators Suite

Body Mass Index (BMI) Tip Calculator Mortgage Affordability Compound Interest Loan Payment Value Added Tax (VAT) Body Fat Percentage Age Calculator Gas Mileage Discount Calculator

Body Mass Index (BMI) Calculator

Your BMI:

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Tip Calculator

Total Bill with Tip:

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Amount Per Person:

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Mortgage Affordability Calculator

Maximum Mortgage Amount You Can Afford:

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Estimated Monthly Payment:

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Compound Interest Calculator

Total Amount after Compound Interest:

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Total Interest Earned:

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Loan Payment Calculator

Estimated Monthly Payment:

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Total Amount Paid:

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Total Interest Paid:

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Value Added Tax (VAT) Calculator

VAT Amount:

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Total Price (Including VAT):

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Body Fat Percentage Calculator (US Navy Method)

Male Female

Estimated Body Fat Percentage:

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Age Calculator

Your Age:

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Gas Mileage Calculator

Your Car's MPG:

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Discount Calculator

Discount Amount:

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Final Price:

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Understanding the Ten Key Calculators

This suite offers a collection of essential tools designed to simplify common financial and personal calculations. Each calculator is built on straightforward mathematical principles, making them accessible and reliable for everyday use.

1. Body Mass Index (BMI) Calculator

Purpose: To estimate body fat based on weight and height. It's a screening tool, not a diagnostic one.
Formula: BMI = weight (kg) / [height (m)]2
Use Case: Individuals looking for a quick health indicator, tracking weight management progress.

2. Tip Calculator

Purpose: To quickly calculate the tip amount and the total bill per person.
Formula:

  • Tip Amount = Bill Amount * (Tip Percentage / 100)
  • Total Bill = Bill Amount + Tip Amount
  • Amount Per Person = Total Bill / Number of People
Use Case: Dining out, estimating service gratuities.

3. Mortgage Affordability Calculator

Purpose: To estimate the maximum mortgage loan one can afford based on income, debts, and market conditions.
Formula: This calculator typically uses the lender's maximum Debt-to-Income (DTI) ratio.

  • Maximum Monthly Debt Payment = Annual Income * (Max DTI Ratio / 100)
  • The calculator then works backward from this maximum monthly payment, considering interest rates and loan terms, to estimate the loan principal. A common formula for monthly mortgage payment (P&I) is: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1], where M is monthly payment, P is principal loan amount, i is monthly interest rate, and n is the number of payments (loan term in months). The calculator estimates P given M.
Use Case: Prospective homebuyers assessing their borrowing capacity.

4. Compound Interest Calculator

Purpose: To calculate the future value of an investment with compound interest.
Formula: A = P (1 + r/n)nt

  • A = the future value of the investment/loan, including interest
  • P = the principal investment amount (the initial deposit or loan amount)
  • r = the annual interest rate (as a decimal)
  • n = the number of times that interest is compounded per year
  • t = the number of years the money is invested or borrowed for
Use Case: Saving, investing, understanding loan growth.

5. Loan Payment Calculator

Purpose: To calculate the fixed periodic payment for a loan.
Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]

  • M = Monthly Payment
  • P = Principal Loan Amount
  • i = Monthly Interest Rate (Annual Rate / 12 / 100)
  • n = Total number of payments (Loan Term in Years * 12)
Use Case: Calculating monthly payments for mortgages, auto loans, personal loans.

6. Value Added Tax (VAT) Calculator

Purpose: To calculate the VAT amount and the total price including VAT.
Formula:

  • VAT Amount = Price Before VAT * (VAT Rate / 100)
  • Total Price = Price Before VAT + VAT Amount
Use Case: Businesses and consumers in regions with VAT to determine tax liabilities.

7. Body Fat Percentage Calculator (US Navy Method)

Purpose: A method to estimate body fat percentage using circumference measurements. Formula: Varies slightly for men and women and requires specific calculations based on height, weight, abdomen, neck (men), and hips (women) measurements in inches. The calculator implements these established formulas.
Use Case: Fitness enthusiasts, individuals tracking body composition.

8. Age Calculator

Purpose: To accurately determine a person's age in years, months, and days.
Formula: Simple date subtraction. Calculate the difference between the birthdate and the current date.
Use Case: Determining age for various legal, personal, or administrative purposes.

9. Gas Mileage Calculator

Purpose: To calculate fuel efficiency in Miles Per Gallon (MPG).
Formula: MPG = Distance Traveled / Fuel Used
Use Case: Tracking vehicle efficiency, estimating fuel costs for travel.

10. Discount Calculator

Purpose: To calculate the amount of discount and the final price after a discount is applied.
Formula:

  • Discount Amount = Original Price * (Discount Percentage / 100)
  • Final Price = Original Price – Discount Amount
Use Case: Shopping, calculating savings on sale items.

function showCalculator(calculatorId) { var calculators = document.getElementsByClassName('calculator-form'); for (var i = 0; i < calculators.length; i++) { calculators[i].classList.remove('active'); } document.getElementById(calculatorId).classList.add('active'); } // — BMI Calculator Logic — function calculateBMI() { var weight = parseFloat(document.getElementById("bmiWeight").value); var height = parseFloat(document.getElementById("bmiHeight").value); var resultElement = document.getElementById("resultBMI"); if (isNaN(weight) || isNaN(height) || height <= 0) { resultElement.innerText = "Please enter valid numbers for weight and height."; return; } var heightInMeters = height / 100; var bmi = weight / (heightInMeters * heightInMeters); bmi = bmi.toFixed(1); resultElement.innerText = bmi; } // — Tip Calculator Logic — function calculateTip() { var bill = parseFloat(document.getElementById("billAmount").value); var tipPercent = parseFloat(document.getElementById("tipPercentage").value); var people = parseInt(document.getElementById("numberOfPeople").value); var resultTipElement = document.getElementById("resultTip"); var resultPerPersonElement = document.getElementById("resultPerPerson"); if (isNaN(bill) || isNaN(tipPercent) || isNaN(people) || people <= 0 || bill < 0 || tipPercent < 0) { resultTipElement.innerText = "Please enter valid numbers."; resultPerPersonElement.innerText = "–"; return; } var tipAmount = bill * (tipPercent / 100); var totalBill = bill + tipAmount; var amountPerPerson = totalBill / people; resultTipElement.innerText = "$" + totalBill.toFixed(2); resultPerPersonElement.innerText = "$" + amountPerPerson.toFixed(2); } // — Mortgage Affordability Calculator Logic — function calculateMortgage() { var income = parseFloat(document.getElementById("annualIncome").value); var dtiRatio = parseFloat(document.getElementById("debtToIncomeRatio").value); var interestRate = parseFloat(document.getElementById("interestRate").value); var loanTerm = parseInt(document.getElementById("loanTerm").value); var downPayment = parseFloat(document.getElementById("downPayment").value); var resultMortgageElement = document.getElementById("resultMortgage"); var resultMonthlyPaymentElement = document.getElementById("resultMonthlyPayment"); if (isNaN(income) || isNaN(dtiRatio) || isNaN(interestRate) || isNaN(loanTerm) || isNaN(downPayment) || income <= 0 || dtiRatio <= 0 || interestRate < 0 || loanTerm <= 0 || downPayment 0 && numberOfPayments > 0) { maxLoanAmount = maxMonthlyPayment * (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1) / (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)); } else if (numberOfPayments > 0) { // 0% interest rate case maxLoanAmount = maxMonthlyPayment * numberOfPayments; } var estimatedMonthlyPayment = 0; if (maxLoanAmount > 0 && monthlyInterestRate > 0 && numberOfPayments > 0) { estimatedMonthlyPayment = maxLoanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1); } else if (maxLoanAmount > 0) { // 0% interest rate case estimatedMonthlyPayment = maxLoanAmount / numberOfPayments; } resultMortgageElement.innerText = "$" + maxLoanAmount.toFixed(2); resultMonthlyPaymentElement.innerText = "$" + estimatedMonthlyPayment.toFixed(2); } // — Compound Interest Calculator Logic — function calculateCompoundInterest() { var principal = parseFloat(document.getElementById("principal").value); var annualRate = parseFloat(document.getElementById("annualRate").value); var years = parseInt(document.getElementById("years").value); var frequency = parseInt(document.getElementById("compoundingFrequency").value); var resultCompoundElement = document.getElementById("resultCompound"); var resultInterestEarnedElement = document.getElementById("resultInterestEarned"); if (isNaN(principal) || isNaN(annualRate) || isNaN(years) || isNaN(frequency) || principal <= 0 || annualRate < 0 || years <= 0 || frequency <= 0) { resultCompoundElement.innerText = "Please enter valid numbers."; resultInterestEarnedElement.innerText = "–"; return; } var ratePerPeriod = (annualRate / 100) / frequency; var numberOfPeriods = years * frequency; var futureValue = principal * Math.pow(1 + ratePerPeriod, numberOfPeriods); var interestEarned = futureValue – principal; resultCompoundElement.innerText = "$" + futureValue.toFixed(2); resultInterestEarnedElement.innerText = "$" + interestEarned.toFixed(2); } // — Loan Payment Calculator Logic — function calculateLoanPayment() { var loanAmount = parseFloat(document.getElementById("loanAmount").value); var annualInterestRateLoan = parseFloat(document.getElementById("annualInterestRateLoan").value); var loanTermYears = parseInt(document.getElementById("loanTermYears").value); var resultLoanPaymentElement = document.getElementById("resultLoanPayment"); var resultTotalPaidElement = document.getElementById("resultTotalPaid"); var resultTotalInterestElement = document.getElementById("resultTotalInterest"); if (isNaN(loanAmount) || isNaN(annualInterestRateLoan) || isNaN(loanTermYears) || loanAmount <= 0 || annualInterestRateLoan < 0 || loanTermYears 0) { monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1); } else { // Handle 0% interest rate monthlyPayment = loanAmount / numberOfPayments; } var totalPaid = monthlyPayment * numberOfPayments; var totalInterest = totalPaid – loanAmount; resultLoanPaymentElement.innerText = "$" + monthlyPayment.toFixed(2); resultTotalPaidElement.innerText = "$" + totalPaid.toFixed(2); resultTotalInterestElement.innerText = "$" + totalInterest.toFixed(2); } // — VAT Calculator Logic — function calculateVAT() { var priceBeforeVAT = parseFloat(document.getElementById("priceBeforeVAT").value); var vatRate = parseFloat(document.getElementById("vatRate").value); var resultVATAmountElement = document.getElementById("resultVATAmount"); var resultTotalPriceVATElment = document.getElementById("resultTotalPriceVAT"); if (isNaN(priceBeforeVAT) || isNaN(vatRate) || priceBeforeVAT < 0 || vatRate < 0) { resultVATAmountElement.innerText = "Please enter valid numbers."; resultTotalPriceVATElment.innerText = "–"; return; } var vatAmount = priceBeforeVAT * (vatRate / 100); var totalPrice = priceBeforeVAT + vatAmount; resultVATAmountElement.innerText = "$" + vatAmount.toFixed(2); resultTotalPriceVATElment.innerText = "$" + totalPrice.toFixed(2); } // — Body Fat Percentage Calculator Logic — function calculateBodyFat() { var gender = document.getElementById("bfGender").value; var weight = parseFloat(document.getElementById("bfWeight").value); // lbs var abdomen = parseFloat(document.getElementById("bfAbdomen").value); // inches var neck = parseFloat(document.getElementById("bfNeck").value); // inches var hips = parseFloat(document.getElementById("bfHips").value); // inches var height = parseFloat(document.getElementById("bfHeight").value); // inches var resultElement = document.getElementById("resultBodyFat"); // Show/Hide neck and hips based on gender if (gender === 'male') { document.getElementById("bfNeckContainer").style.display = 'flex'; document.getElementById("bfHipsContainer").style.display = 'none'; if (isNaN(weight) || isNaN(abdomen) || isNaN(neck) || isNaN(height) || weight <= 0 || abdomen <= 0 || neck <= 0 || height <= 0) { resultElement.innerText = "Please enter valid numbers for male."; return; } var circumference = abdomen – neck; var bf = 86.010 * Math.log(circumference) – 77.492 * Math.log(height) + 36.765; } else { // female document.getElementById("bfNeckContainer").style.display = 'flex'; document.getElementById("bfHipsContainer").style.display = 'flex'; if (isNaN(weight) || isNaN(abdomen) || isNaN(neck) || isNaN(hips) || isNaN(height) || weight <= 0 || abdomen <= 0 || neck <= 0 || hips <= 0 || height today) { resultElement.innerText = "Birthdate cannot be in the future."; return; } var age = today.getFullYear() – birthDate.getFullYear(); var monthDiff = today.getMonth() – birthDate.getMonth(); if (monthDiff < 0 || (monthDiff === 0 && today.getDate() < birthDate.getDate())) { age–; } resultElement.innerText = age + " years"; } // — Gas Mileage Calculator Logic — function calculateGasMileage() { var distance = parseFloat(document.getElementById("distanceTraveled").value); var fuel = parseFloat(document.getElementById("fuelUsed").value); var resultElement = document.getElementById("resultGasMileage"); if (isNaN(distance) || isNaN(fuel) || distance <= 0 || fuel <= 0) { resultElement.innerText = "Please enter valid numbers for distance and fuel."; return; } var mpg = distance / fuel; resultElement.innerText = mpg.toFixed(2) + " MPG"; } // — Discount Calculator Logic — function calculateDiscount() { var originalPrice = parseFloat(document.getElementById("originalPrice").value); var discountPercentage = parseFloat(document.getElementById("discountPercentage").value); var resultDiscountAmountElement = document.getElementById("resultDiscountAmount"); var resultFinalPriceElement = document.getElementById("resultFinalPrice"); if (isNaN(originalPrice) || isNaN(discountPercentage) || originalPrice <= 0 || discountPercentage 100) { resultDiscountAmountElement.innerText = "Please enter valid numbers."; resultFinalPriceElement.innerText = "–"; return; } var discountAmount = originalPrice * (discountPercentage / 100); var finalPrice = originalPrice – discountAmount; resultDiscountAmountElement.innerText = "$" + discountAmount.toFixed(2); resultFinalPriceElement.innerText = "$" + finalPrice.toFixed(2); } // Set today's date for the age calculator on load window.onload = function() { var todayInput = document.getElementById('todayDate'); if (todayInput) { var today = new Date(); var dd = String(today.getDate()).padStart(2, '0'); var mm = String(today.getMonth() + 1).padStart(2, '0'); // January is 0! var yyyy = today.getFullYear(); todayInput.value = yyyy + '-' + mm + '-' + dd; } // Trigger the initial display for the first calculator showCalculator(document.getElementById("calculator-select").value); };

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