DATE DIFF

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

function setToday() {
    const today = new Date().toISOString().slice(0,10);
    document.getElementById('dateA').value = today;
    calculate();
  }

  function swap() {
    const a = document.getElementById('dateA').value, b = document.getElementById('dateB').value;
    document.getElementById('dateA').value = b; document.getElementById('dateB').value = a;
    calculate();
  }

  function toggleTime() {
    document.getElementById('timeRow').classList.toggle('hidden', !document.getElementById('includeTime').checked);
    calculate();
  }

  function businessDays(d1, d2) {
    if (d1 > d2) [d1,d2] = [d2,d1];
    let count = 0, cur = new Date(d1);
    while (cur <= d2) {
      const day = cur.getDay();
      if (day !== 0 && day !== 6) count++;
      cur.setDate(cur.getDate() + 1);
    }
    return count;
  }

  function calculate() {
    const da = document.getElementById('dateA').value, db = document.getElementById('dateB').value;
    if (!da || !db) { document.getElementById('results').classList.add('hidden'); return; }
    const incTime = document.getElementById('includeTime').checked;
    const ta = incTime ? document.getElementById('timeA').value : '00:00';
    const tb = incTime ? document.getElementById('timeB').value : '00:00';
    let dtA = new Date(`${da}T${ta}`), dtB = new Date(`${db}T${tb}`);
    const swapped = dtA > dtB;
    if (swapped) [dtA, dtB] = [dtB, dtA];

    const diffMs = dtB - dtA;
    const diffSec = Math.floor(diffMs / 1000);
    const diffMin = Math.floor(diffSec / 60);
    const diffHrs = Math.floor(diffMin / 60);
    const diffDays = Math.floor(diffHrs / 24);
    const diffWeeks = Math.floor(diffDays / 7);

    // Years/months
    let yrs = dtB.getFullYear() - dtA.getFullYear();
    let mos = dtB.getMonth() - dtA.getMonth();
    let dys = dtB.getDate() - dtA.getDate();
    if (dys < 0) { mos--; dys += new Date(dtB.getFullYear(), dtB.getMonth(), 0).getDate(); }
    if (mos < 0) { yrs--; mos += 12; }

    document.getElementById('statYears').textContent = yrs;
    document.getElementById('statMonths').textContent = mos;
    document.getElementById('statWeeks').textContent = diffWeeks;
    document.getElementById('statDays').textContent = dys;

    document.getElementById('bDays').textContent = diffDays.toLocaleString();
    document.getElementById('bWeeks').textContent = diffWeeks.toLocaleString();
    document.getElementById('bHours').textContent = diffHrs.toLocaleString();
    document.getElementById('bMins').textContent = diffMin.toLocaleString();
    document.getElementById('bSecs').textContent = diffSec.toLocaleString();
    document.getElementById('bBiz').textContent = businessDays(dtA, dtB).toLocaleString();

    const parts = [];
    if (yrs) parts.push(`${yrs} year${yrs!==1?'s':''}`);
    if (mos) parts.push(`${mos} month${mos!==1?'s':''}`);
    if (dys) parts.push(`${dys} day${dys!==1?'s':''}`);
    document.getElementById('resultSummary').innerHTML = `${swapped?'(dates swapped) ':''}<span>${parts.join(', ') || '0 days'}</span> between the two dates.`;
    document.getElementById('results').classList.remove('hidden');
  }

  // Default: today and 1 year ago
  const today = new Date();
  const oneYearAgo = new Date(today); oneYearAgo.setFullYear(oneYearAgo.getFullYear() - 1);
  document.getElementById('dateA').value = oneYearAgo.toISOString().slice(0,10);
  document.getElementById('dateB').value = today.toISOString().slice(0,10);
  calculate();