Measure the precise duration between two date-times, down to seconds.
This calculator measures the exact span between two date-time instants by differencing their UTC millisecond timestamps. That makes it accurate across month and year boundaries (which have unequal lengths) and correct across daylight-saving transitions when both times share the same local timezone. The total-second count is then decomposed into days, hours, minutes and seconds for display.
Duration
Duration (ms) = end timestamp − start timestamp
Decomposition
days = floor(|Δt_s| / 86400), hours = floor((|Δt_s| mod 86400) / 3600), ...
The Date Duration Calculator works at day granularity and is designed for 'how many days between two dates' questions. This calculator works at second granularity and is designed for questions like 'how long did this process take' where hours and minutes matter.
Use ISO 8601 format: YYYY-MM-DDTHH:mm, for example 2025-06-15T08:30. Most modern browsers also accept 'June 15, 2025 08:30' but the ISO format is unambiguous.
Yes, because both timestamps are converted to UTC milliseconds before differencing. A 2-hour span from 1:00 AM to 3:00 AM on a spring-forward night will correctly compute as 1 hour of elapsed wall-clock time.
The duration is still computed but shown as negative. This is useful when you need to know 'how far in the past' a timestamp is.