Unix Calculator

    JavaScript Unix Timestamps Cheatsheet

    Last updated May 2026

    JavaScript Timestamps Cheatsheet

    Every timestamp operation you need. Print or save as PDF.

    Get Current Timestamp

    // Unix seconds (integer)
Math.floor(Date.now() / 1000)
// → 1733529600

// Unix milliseconds
Date.now()
// → 1733529600000

// As Date object
new Date()
// → Sat Dec 07 2024...

// High resolution (not Unix)
performance.now()
// → 1234.567 (ms since page load)

    Timestamp → Human Readable

    // Seconds → Date object
new Date(ts * 1000)

// Milliseconds → Date object  
new Date(tsMs)

// → ISO 8601 string
new Date(ts * 1000).toISOString()
// "2024-12-07T04:00:00.000Z"

// → UTC string
new Date(ts * 1000).toUTCString()
// "Sat, 07 Dec 2024 04:00:00 GMT"

// → Local string
new Date(ts * 1000).toLocaleString()

    Date → Timestamp

    // Date string → Unix seconds
Math.floor(new Date('2024-12-07').getTime() / 1000)
// → 1733529600

// Date object → Unix seconds
Math.floor(someDate.getTime() / 1000)

// ISO string → Unix ms
new Date('2024-12-07T04:00:00Z').getTime()
// → 1733529600000

// Specific date → Unix seconds
Math.floor(new Date(2024, 11, 7).getTime() / 1000)
// Note: month is 0-indexed! Dec = 11

    Timezone-Aware Formatting

    const date = new Date(1733529600 * 1000);

// Intl.DateTimeFormat (recommended)
new Intl.DateTimeFormat('en-US', {
  timeZone: 'America/New_York',
  dateStyle: 'full',
  timeStyle: 'long',
}).format(date)

// Multiple timezones
['UTC','America/New_York','Asia/Tokyo']
  .map(tz => ({
    tz,
    time: date.toLocaleString('en-US', { timeZone: tz })
  }))

    Date Arithmetic

    const now = Math.floor(Date.now() / 1000);

// Add time (in seconds)
const ONE_HOUR  = 3600;
const ONE_DAY   = 86400;
const ONE_WEEK  = 604800;
const ONE_MONTH = 2592000; // ~30 days

const tomorrow = now + ONE_DAY;
const lastWeek = now - ONE_WEEK;

// Duration between two timestamps
const diff = ts2 - ts1; // seconds
const days  = Math.floor(diff / 86400);
const hours = Math.floor((diff % 86400) / 3600);
const mins  = Math.floor((diff % 3600) / 60);

    ⚠️ Common Mistakes

    // ✗ WRONG — date shows 1970
new Date(1733529600)
// ✓ RIGHT — multiply seconds by 1000
new Date(1733529600 * 1000)

// ✗ WRONG — month 12 = January next year
new Date(2024, 12, 1)
// ✓ RIGHT — December = 11
new Date(2024, 11, 1)

// ✗ WRONG — float loses precision at huge scales
const ts = parseFloat("1733529600.999")
// ✓ RIGHT — use BigInt for nanoseconds-scale literals
const ns = BigInt("1733529600999000000")

    Format Quick Reference

    DigitsUnitExample
    10 digitsSeconds1733529600
    13 digitsMilliseconds1733529600000
    16 digitsMicroseconds1733529600000000
    19 digitsNanoseconds1733529600000000000
    // Auto-detect format
function detectFormat(ts) {
  const d = String(Math.abs(ts)).replace('.','').length
  if (d <= 10) return 'seconds'
  if (d <= 13) return 'milliseconds'
  if (d <= 16) return 'microseconds'
  return 'nanoseconds'
}

    JWT / Session Expiry

    const now = Math.floor(Date.now() / 1000);

// Check if token is expired
const isExpired = payload.exp < now;

// Time until expiry
const secondsLeft = payload.exp - now;
const isExpiringSoon = secondsLeft < 300; // 5 min

// Create expiry timestamp
const expiry = now + 3600; // 1 hour from now

// Session timeout
const SESSION_TTL = 30 * 60; // 30 minutes
const sessionExpiry = now + SESSION_TTL;
const isSessionValid = now < sessionExpiry;

    Relative Time Display

    function timeAgo(ts) {
  const diff = Math.floor(Date.now()/1000) - ts;
  if (diff < 60)   return 'just now';
  if (diff < 3600) return Math.floor(diff/60) + 'm ago';
  if (diff < 86400)return Math.floor(diff/3600) + 'h ago';
  return Math.floor(diff/86400) + 'd ago';
}

// Or use Intl.RelativeTimeFormat
const rtf = new Intl.RelativeTimeFormat('en');
rtf.format(-1, 'day')   // "1 day ago"
rtf.format(2, 'hour')   // "in 2 hours"

    Useful Constants

    const SECOND = 1;
const MINUTE = 60;
const HOUR   = 3_600;
const DAY    = 86_400;
const WEEK   = 604_800;
const MONTH  = 2_592_000;  // 30 days
const YEAR   = 31_536_000; // 365 days

// Famous timestamps
const UNIX_EPOCH  = 0;          // 1970-01-01
const Y2K         = 946684800;  // 2000-01-01
const Y2038_LIMIT = 2147483647; // 2038-01-19
const MAX_SAFE_MS = Number.MAX_SAFE_INTEGER;
// = 9007199254740991

    unixcalculator.com — Free developer tools & timestamp reference · /tools/timestamp-debugger · /tools/jwt-decoder