EMI Calculator

Standalone, zero-dependency JavaScript implementation powering this tool. Free to inspect, copy, and build upon.

function inFmt(n) { return Math.round(n).toLocaleString('en-IN'); }
  function fmtRs(n) { return '₹' + inFmt(n); }

  // Link input <-> slider
  function linkInputSlider(inputId, sliderId, onChange) {
    const inp = document.getElementById(inputId);
    const sl = document.getElementById(sliderId);
    inp.addEventListener('input', () => { sl.value = inp.value; onChange(); });
    sl.addEventListener('input', () => { inp.value = sl.value; onChange(); });
  }

  linkInputSlider('inp-amount', 'sl-amount', calculate);
  linkInputSlider('inp-rate', 'sl-rate', calculate);
  linkInputSlider('inp-tenure', 'sl-tenure', calculate);

  let fullAmort = [];
  let showingAll = false;

  document.getElementById('show-all-btn').addEventListener('click', () => {
    showingAll = !showingAll;
    renderAmort();
    document.getElementById('show-all-btn').textContent = showingAll ? 'Show less' : 'Show all months';
  });

  function calculate() {
    const P = parseFloat(document.getElementById('inp-amount').value);
    const annualRate = parseFloat(document.getElementById('inp-rate').value);
    const n = parseInt(document.getElementById('inp-tenure').value);

    // Tenure hint
    const yrs = Math.floor(n / 12);
    const mos = n % 12;
    let hint = '';
    if (yrs > 0 && mos > 0) hint = `${yrs} yr ${mos} mo`;
    else if (yrs > 0) hint = `${yrs} year${yrs > 1 ? 's' : ''}`;
    else hint = `${mos} month${mos > 1 ? 's' : ''}`;
    document.getElementById('tenure-years').textContent = hint;

    if (!P || !annualRate || !n || P <= 0 || annualRate <= 0 || n <= 0) return;

    const r = annualRate / 12 / 100;
    const emi = P * r * Math.pow(1 + r, n) / (Math.pow(1 + r, n) - 1);
    const totalPayable = emi * n;
    const totalInterest = totalPayable - P;
    const intPct = (totalInterest / P) * 100;

    document.getElementById('emi-big').textContent = fmtRs(emi);
    document.getElementById('val-principal').textContent = fmtRs(P);
    document.getElementById('val-interest').textContent = fmtRs(totalInterest);
    document.getElementById('val-total').textContent = fmtRs(totalPayable);
    document.getElementById('val-int-pct').textContent = intPct.toFixed(1) + '%';

    // Build amort schedule
    fullAmort = [];
    let balance = P;
    for (let m = 1; m <= n; m++) {
      const interestPart = balance * r;
      const principalPart = emi - interestPart;
      balance -= principalPart;
      fullAmort.push({
        month: m,
        principal: principalPart,
        interest: interestPart,
        balance: Math.max(0, balance)
      });
    }

    showingAll = false;
    document.getElementById('show-all-btn').textContent = 'Show all months';
    renderAmort();
    const btn = document.getElementById('show-all-btn');
    btn.classList.toggle('hidden', fullAmort.length <= 12);
  }

  function renderAmort() {
    const rows = showingAll ? fullAmort : fullAmort.slice(0, 12);
    const tbody = document.getElementById('amort-body');
    tbody.innerHTML = rows.map(r =>
      `<tr>
        <td>${r.month}</td>
        <td>${inFmt(r.principal)}</td>
        <td>${inFmt(r.interest)}</td>
        <td>${inFmt(r.balance)}</td>
      </tr>`
    ).join('');
  }

  calculate();