Mortgage Calculator

`); printWindow.document.close(); printWindow.print(); });exportCsvBtn.addEventListener('click', () => { const rows = [["Year", "Month", "Principal", "Interest", "Remaining Balance"]]; amortizationTableBody.querySelectorAll('details').forEach(detail => { const year = detail.querySelector('summary .summary-year').textContent; detail.querySelectorAll('.monthly-table tbody tr').forEach(row => { const cells = Array.from(row.querySelectorAll('td')).map(td => { const text = td.textContent.replace(/[^0-9A-Za-z\s.]/g, ''); return `"${text.replace(/"/g, '""')}"`; }); rows.push([year, ...cells]); }); }); const csvContent = "data:text/csv;charset=utf-8," + rows.map(e => e.join(",")).join("\n"); const link = document.createElement("a"); link.setAttribute("href", encodeURI(csvContent)); link.setAttribute("download", "amortization_schedule.csv"); document.body.appendChild(link); link.click(); document.body.removeChild(link); });// --- CORE LOGIC --- function updateMonthlyInputs() { taxMonthlyInput.value = formatInput(parseCurrency(propertyTaxInput.value)); insMonthlyInput.value = formatInput(parseCurrency(homeInsuranceInput.value)); pmiMonthlyInput.value = formatInput(parseCurrency(pmiInput.value)); hoaMonthlyInput.value = formatInput(parseCurrency(hoaInput.value)); taxMonthlyDisplay.textContent = formatCurrency(parseCurrency(taxMonthlyInput.value)); insMonthlyDisplay.textContent = formatCurrency(parseCurrency(insMonthlyInput.value)); pmiMonthlyDisplay.textContent = formatCurrency(parseCurrency(pmiMonthlyInput.value)); hoaMonthlyDisplay.textContent = formatCurrency(parseCurrency(hoaMonthlyInput.value)); }function getFormValues() { const homePrice = parseCurrency(homePriceInput.value); const dpAmount = parseCurrency(dpAmountInput.value); const loanAmount = Math.max(0, homePrice - dpAmount); const startDate = startDateInput.value ? new Date(startDateInput.value) : new Date(); const oneTimeDate = oneTimeDateInput.value ? new Date(oneTimeDateInput.value) : new Date(); return { homePrice, dpAmount, dpPercent: parseFloat(dpPercentInput.value) || 0, loanTerm: parseInt(loanTermSelect.value, 10), annualRate: parseFloat(interestRateInput.value) || 0, loanAmount, taxMonthly: parseCurrency(propertyTaxInput.value), insMonthly: parseCurrency(homeInsuranceInput.value), pmiMonthly: parseCurrency(pmiInput.value), hoaMonthly: parseCurrency(hoaInput.value), extraMonthly: parseCurrency(extraMonthlyInput.value), extraYearly: parseCurrency(extraYearlyInput.value), oneTimeAmount: parseCurrency(oneTimeAmountInput.value), oneTimeDate, startDate }; }function calculateAndDisplay() { loadingSpinner.classList.add('active'); setTimeout(() => { const form = getFormValues(); const monthlyRate = form.annualRate / 1200; const numPayments = form.loanTerm * 12;let pni = 0; if (form.loanAmount > 0 && numPayments > 0) { if (monthlyRate > 0) { pni = form.loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numPayments)) / (Math.pow(1 + monthlyRate, numPayments) - 1); } else { pni = form.loanAmount / numPayments; } } const pniDisplay = Number(pni.toFixed(2)); pniDisplayEl.textContent = formatCurrency(pniDisplay); document.getElementById('pni-monthly').value = formatInput(pniDisplay); updateMonthlyInputs();const payments = { pni: pniDisplay, taxMonthly: form.taxMonthly, insMonthly: form.insMonthly, pmiMonthly: form.pmiMonthly, hoaMonthly: form.hoaMonthly };const amortizationData = generateAmortization( form.loanAmount, monthlyRate, pni, numPayments, form.extraMonthly, form.extraYearly, form.oneTimeAmount, form.oneTimeDate, form.startDate ); updateUI(payments, form, amortizationData); loadingSpinner.classList.remove('active'); doughnutChartEl.classList.add('updated'); setTimeout(() => doughnutChartEl.classList.remove('updated'), 300); }, 100); }function generateAmortization(principal, monthlyRate, pni, totalPayments, extraMonthly, extraYearly, oneTimeAmount, oneTimeDate, startDate) { if (principal <= 0 || totalPayments <= 0) { return { yearlyData: {}, monthlyData: [], totalInterest: 0, firstPaymentDate: new Date(), lastPaymentDate: new Date() }; }let balance = principal; let totalInterest = 0; const firstPaymentDate = new Date(startDate.getFullYear(), startDate.getMonth() + 1, 1); let currentDate = new Date(firstPaymentDate); let lastPaymentDate = currentDate; const monthlyData = []; const yearlyData = {}; let oneTimeApplied = false;for (let i = 0; i < totalPayments && balance > 0.01; i++) { const year = currentDate.getFullYear(); const isYearStart = currentDate.getMonth() === 0;const interestPayment = balance * monthlyRate; let principalPayment = pni - interestPayment + extraMonthly;if (isYearStart && extraYearly > 0 && currentDate > firstPaymentDate) { principalPayment += extraYearly; }if (!oneTimeApplied && oneTimeAmount > 0 && currentDate >= oneTimeDate) { principalPayment += oneTimeAmount; oneTimeApplied = true; }if (principalPayment > balance) { principalPayment = balance; }balance -= principalPayment; totalInterest += interestPayment; lastPaymentDate = new Date(currentDate);monthlyData.push({ date: new Date(currentDate), interest: Number(interestPayment.toFixed(2)), principal: Number(principalPayment.toFixed(2)), balance: Number(Math.max(balance, 0).toFixed(2)) });if (!yearlyData[year]) { yearlyData[year] = { months: [], totalPrincipal: 0, totalInterest: 0, endBalance: 0 }; } yearlyData[year].months.push(monthlyData[monthlyData.length - 1]); yearlyData[year].totalPrincipal += principalPayment; yearlyData[year].totalInterest += interestPayment; yearlyData[year].endBalance = Math.max(balance, 0);currentDate.setMonth(currentDate.getMonth() + 1); }Object.keys(yearlyData).forEach(year => { yearlyData[year].totalPrincipal = Number(yearlyData[year].totalPrincipal.toFixed(2)); yearlyData[year].totalInterest = Number(yearlyData[year].totalInterest.toFixed(2)); yearlyData[year].endBalance = Number(yearlyData[year].endBalance.toFixed(2)); });return { yearlyData, monthlyData, totalInterest: Number(totalInterest.toFixed(2)), firstPaymentDate, lastPaymentDate }; }function updateUI(payments, form, amortizationData) { const { pni, taxMonthly, insMonthly, pmiMonthly, hoaMonthly } = payments; const { yearlyData, monthlyData, totalInterest, firstPaymentDate, lastPaymentDate } = amortizationData;dynamicRateEl.textContent = dynamicRateAmortEl.textContent = form.annualRate.toFixed(3); const totalMonthly = Number((pni + taxMonthly + insMonthly + pmiMonthly + hoaMonthly).toFixed(2)); totalMonthlyPaymentEl.textContent = formatCurrency(totalMonthly);doughnutChartEl.innerHTML = `${formatCurrency(totalMonthly).replace('.00', '')}/mo`; if (totalMonthly > 0) { const pniP = (pni / totalMonthly) * 100; const taxP = (taxMonthly / totalMonthly) * 100; const insP = (insMonthly / totalMonthly) * 100; const pmiP = (pmiMonthly / totalMonthly) * 100; doughnutChartEl.style.backgroundImage = `conic-gradient( var(--br-chart-pni) 0% ${pniP}%, var(--br-chart-tax) ${pniP}% ${pniP + taxP}%, var(--br-chart-ins) ${pniP + taxP}% ${pniP + taxP + insP}%, var(--br-chart-pmi) ${pniP + taxP + insP}% ${pniP + taxP + insP + pmiP}%, var(--br-chart-hoa) ${pniP + taxP + insP + pmiP}% 100% )`; } else { doughnutChartEl.style.backgroundImage = 'conic-gradient(#eee 0% 100%)'; }const payoffDateStr = lastPaymentDate.toLocaleString('default', { month: 'long', year: 'numeric' }); summaryLoanAmountEl.textContent = formatCurrency(form.loanAmount); summaryTotalInterestEl.textContent = formatCurrency(totalInterest); summaryTotalCostEl.textContent = formatCurrency(Number((form.loanAmount + totalInterest).toFixed(2))); summaryPayoffDateEl.textContent = payoffDateStr; firstPaymentDateEl.textContent = firstPaymentDate.toLocaleString('default', { month: 'long', year: 'numeric' }); lastPaymentDateEl.textContent = payoffDateStr;updateAmortizationGraph(yearlyData, form.loanAmount, totalInterest); updateAmortizationTable(yearlyData); }function updateAmortizationGraph(yearlyData, loanAmount, totalInterest) { const svg = document.getElementById('amortization-chart-svg'); svg.innerHTML = ''; if (Object.keys(yearlyData).length === 0 || loanAmount <= 0) { svg.innerHTML = 'No data to display'; return; }const allMonths = Object.values(yearlyData).flatMap(y => y.months); if (allMonths.length === 0) return;const width = 400, height = 220, m = { top: 20, right: 20, bottom: 35, left: 50 }; const w = width - m.left - m.right, h = height - m.top - m.bottom; const maxY = Math.max(loanAmount, totalInterest, 1);const g = document.createElementNS("http://www.w3.org/2000/svg", "g"); g.setAttribute("transform", `translate(${m.left},${m.top})`); svg.appendChild(g);const xScale = i => (i / (allMonths.length - 1)) * w; const yScale = v => h - (v / maxY) * h;const createPath = (data, color) => { const path = document.createElementNS("http://www.w3.org/2000/svg", "path"); path.setAttribute('d', `M0,${yScale(data[0])} ` + data.slice(1).map((d, i) => `L${xScale(i + 1)},${yScale(d)}`).join(' ')); path.setAttribute('class', 'line'); path.style.stroke = color; path.style.strokeWidth = '2.5'; path.style.opacity = '0.9'; return path; };let cumulativePrincipal = 0, cumulativeInterest = 0; const balanceData = allMonths.map(d => d.balance < 0 ? 0 : d.balance); const principalData = allMonths.map(d => (cumulativePrincipal += d.principal, Math.min(cumulativePrincipal, maxY))); const interestData = allMonths.map(d => (cumulativeInterest += d.interest, Math.min(cumulativeInterest, maxY)));[createPath(balanceData, 'var(--br-chart-balance)'), createPath(principalData, 'var(--br-chart-principal)'), createPath(interestData, 'var(--br-chart-interest)')].forEach(path => g.appendChild(path));for (let i = 0; i <= 5; i++) { const y = h * (i / 5); const line = document.createElementNS("http://www.w3.org/2000/svg", "line"); line.setAttribute('x1', 0); line.setAttribute('x2', w); line.setAttribute('y1', y); line.setAttribute('y2', y); line.setAttribute('class', 'grid'); g.appendChild(line); const text = document.createElementNS("http://www.w3.org/2000/svg", "text"); text.setAttribute('x', -10); text.setAttribute('y', y + 4); text.setAttribute('class', 'axis-label'); text.setAttribute('text-anchor', 'end'); text.textContent = `$${(maxY * (1 - i / 5) / 1000).toFixed(0)}k`; g.appendChild(text); }const yearKeys = Object.keys(yearlyData).sort(); const step = Math.max(1, Math.ceil(yearKeys.length / 6)); for (let i = 0; i < yearKeys.length; i += step) { const year = yearKeys[i]; const monthIndex = allMonths.findIndex(d => d.date.getFullYear() == year); if (monthIndex < 0) continue; const x = xScale(monthIndex); const line = document.createElementNS("http://www.w3.org/2000/svg", "line"); line.setAttribute('x1', x); line.setAttribute('x2', x); line.setAttribute('y1', 0); line.setAttribute('y2', h); line.setAttribute('class', 'grid'); g.appendChild(line); const text = document.createElementNS("http://www.w3.org/2000/svg", "text"); text.setAttribute('x', x); text.setAttribute('y', h + 20); text.setAttribute('class', 'axis-label'); text.setAttribute('text-anchor', 'middle'); text.textContent = year; g.appendChild(text); } }function updateAmortizationTable(yearlyData) { amortizationTableBody.innerHTML = ''; Object.keys(yearlyData).sort().forEach(year => { const yearData = yearlyData[year]; const details = document.createElement('details'); details.innerHTML = `

${year} ${formatCurrency(yearData.totalPrincipal)} ${formatCurrency(yearData.totalInterest)} ${formatCurrency(yearData.endBalance)}

`; amortizationTableBody.appendChild(details); }); }calculateAndDisplay(); });