offsetAt

Module Export

instant | date |> (zone: Timezone) => minutes

The UTC offset in force at a given instant, in the given timezone.

Remarks

The offset at that instant — not the zone’s current offset. A zone observing daylight saving has at least two offsets during a year, and its historical rules may differ from today’s, so an offset is only meaningful with respect to a point in time.

Returned as a minutes duration rather than a number, because not every offset is a whole number of hours: India is UTC+05:30 and Nepal UTC+05:45.

Reaching for this to do your own calendar arithmetic is usually a mistake — applying a single offset across a range breaks at every transition. Prefer startOf and periods, which resolve each boundary individually.

Examples

import 'calendar'

from 2026-07-15T12:00:00Z offsetAt 'Europe/Stockholm'

// Returns:
// Summer time
120 minutes

import 'calendar'

from 2026-01-15T12:00:00Z offsetAt 'Europe/Stockholm'

// Returns:
// Standard time
60 minutes

Historical rules are honoured — Sweden observed no summer time in 1970:

import 'calendar'

from 1970-07-15T12:00:00Z offsetAt 'Europe/Stockholm'

// Returns:
60 minutes

Offsets need not be whole hours:

import 'calendar'

from 2026-07-15T12:00:00Z offsetAt 'Asia/Kolkata'

// Returns:
330 minutes