Duration Calculator

2024-01-31T00:00:00.000Z to 2024-03-01T00:00:00.000Z is 0 year(s), 1 month(s), 1 day(s), 0:00:00.

How it works

• Measured the span between the two instants with the later instant as the end.
• Counted whole calendar years, then whole calendar months with the day clamped to the target month (so Jan 31 + 1 month is Feb 28/29).
• Counted the remaining whole days, hours, minutes and seconds.

• The direction reflects whether the end is after or before the start.

Methodology

1. Parse the start and end (or the applied components) as absolute instants.
2. For a span, count whole calendar years and months using real month lengths and day-clamping, then the remaining days and time.
3. For an applied duration, add calendar years and months with day-clamping, then the fixed-length weeks, days and time units.

Time model

• Time source: an explicit reference supplied by the visitor.
• Timezone: Instants are absolute and timezone-independent; a date-only input is read as UTC midnight.
• Locale: ISO-8601 instants and durations only; no locale-specific formatting.
• Daylight saving: Spans are measured between absolute instants, so daylight-saving transitions never change the result.
• Reference date: A start instant is required; the end or the applied components are supplied explicitly.

Usage

1. Enter the start instant.
2. Enter an end instant to measure the duration, or fill in any duration component to apply it.
3. Read the calendar breakdown, the totals and the ISO-8601 duration.

Examples

These are examples, not current values: they use fixed inputs, while the interactive tool computes live results in your browser.

Across a leap day

{
  "start": "2024-01-31T00:00:00Z",
  "end": "2024-03-01T00:00:00Z"
}

Across a year boundary

{
  "start": "2023-01-31T00:00:00Z",
  "end": "2024-03-01T00:00:00Z"
}

Apply one calendar month to Jan 31

{
  "start": "2024-01-31T00:00:00Z",
  "months": 1
}

Apply a mixed duration

{
  "start": "2026-01-01T00:00:00Z",
  "years": 1,
  "months": 2,
  "days": 3,
  "hours": 4,
  "minutes": 5,
  "seconds": 6
}

Limitations

Why months are not 30 days

Calendar months have different lengths. This tool advances by whole months using the real calendar and clamps the day, rather than multiplying a fixed 30-day figure.