About

India Standard Time (IST, UTC+5:30) maintains a fixed offset year-round. The United States spans six primary civil time zones, four of which observe Daylight Saving Time from the second Sunday in March to the first Sunday in November. A naive conversion using static offsets (e.g., "subtract 10.5 hours for EST") fails during DST transitions, producing errors of ±1 hr. This tool uses the browser's native IANA timezone database via Intl.DateTimeFormat, which tracks historical and current DST rules per zone. It handles edge cases such as Arizona (no DST), Hawaii (no DST), and the varying US territories. Miscalculating a meeting time across these zones costs real productivity. This converter eliminates that risk.

The conversion is bidirectional. Select a time in India and see all US zones, or pick a US zone and see the corresponding IST. Note: this tool assumes standard civil time rules as maintained by the IANA tz database. Territories with non-standard rules (e.g., Navajo Nation within Arizona) follow their respective IANA entries.

Formulas

Timezone conversion uses the projection of a timestamp from one IANA zone to another. The browser's Intl.DateTimeFormat API resolves the correct offset, including DST, for any given moment:

T_US = project(T_IST, tz_target)

Where T_IST is the input timestamp constructed in Asia/Kolkata, and tz_target is the IANA identifier of the target US zone. Internally, the operation is equivalent to:

T_US = T_UTC + offset(tz_target, T_UTC)

Where offset(tz, t) is a piecewise function that returns the zone's standard or daylight offset depending on whether t falls within the DST window. For IST, the offset is constant at +5:30. For US Eastern during DST: −4:00; outside DST: −5:00.

offset(ET, t) = {

−4 hr if t ∈ DST window−5 hr otherwise

Where T_UTC = Universal Coordinated Time, offset = zone-specific offset function, tz_target = IANA timezone identifier (e.g., America/New_York), and project = the formatting operation that expresses a UTC instant in local terms.

Reference Data

US Time Zone	IANA Identifier	UTC Offset (Standard)	UTC Offset (DST)	DST Observed	Offset from IST (Std)	Offset from IST (DST)	Major Cities
Eastern (ET)	America/New_York	UTC−5	UTC−4	Yes	−10:30 hr	−9:30 hr	New York, Miami, Atlanta, Boston
Central (CT)	America/Chicago	UTC−6	UTC−5	Yes	−11:30 hr	−10:30 hr	Chicago, Houston, Dallas, Austin
Mountain (MT)	America/Denver	UTC−7	UTC−6	Yes	−12:30 hr	−11:30 hr	Denver, Phoenix*, Salt Lake City
Mountain (AZ, no DST)	America/Phoenix	UTC−7	UTC−7	No	−12:30 hr	−12:30 hr	Phoenix, Tucson, Mesa
Pacific (PT)	America/Los_Angeles	UTC−8	UTC−7	Yes	−13:30 hr	−12:30 hr	Los Angeles, San Francisco, Seattle
Alaska (AKT)	America/Anchorage	UTC−9	UTC−8	Yes	−14:30 hr	−13:30 hr	Anchorage, Fairbanks, Juneau
Hawaii (HST)	Pacific/Honolulu	UTC−10	UTC−10	No	−15:30 hr	−15:30 hr	Honolulu, Hilo, Kailua
Samoa (SST)	Pacific/Pago_Pago	UTC−11	UTC−11	No	−16:30 hr	−16:30 hr	Pago Pago
Chamorro (ChST)	Pacific/Guam	UTC+10	UTC+10	No	+4:30 hr	+4:30 hr	Hagatna, Saipan
Atlantic (AST)	America/Virgin	UTC−4	UTC−4	No	−9:30 hr	−9:30 hr	Charlotte Amalie, St. Croix
IST Reference	Asia/Kolkata	UTC+5:30	UTC+5:30	No	0	0	Mumbai, Delhi, Bangalore, Chennai

Frequently Asked Questions

The converter uses the browser's native Intl.DateTimeFormat API with IANA timezone identifiers. This API consults the compiled ICU timezone database, which contains all historical and current DST transition rules for each zone. When you select a date that falls within a DST window (second Sunday of March to first Sunday of November for most US zones), the offset automatically adjusts by +1 hour. You do not need to manually account for DST.

Arizona (IANA: America/Phoenix) does not observe DST, maintaining UTC−7 year-round. During summer, when the rest of Mountain Time shifts to UTC−6, Arizona remains at UTC−7, effectively aligning with Pacific Daylight Time. This means the IST-to-Arizona offset is a constant −12:30 hours regardless of season, while IST-to-Denver varies between −12:30 (winter) and −11:30 (summer).

The converter displays the full date alongside the time. If a 9:00 AM IST Monday converts to 10:30 PM ET Sunday, the result clearly shows the day shift. The date indicator changes color to alert you when the converted time falls on a different calendar day than the source.

Yes. IST is UTC+5:30, one of several zones worldwide with a non-hour offset. The Intl API handles this natively. This is why IST conversions produce times ending in :30 or :00 relative to US zones (which use whole-hour offsets), e.g., 12:00 PM IST = 1:30 AM ET (standard).

Yes. The tool includes Chamorro Standard Time (Pacific/Guam, UTC+10), Atlantic Standard Time (America/Virgin, UTC−4), and Samoa Standard Time (Pacific/Pago_Pago, UTC−11). None of these territories observe DST. Guam is notably ahead of IST by 4:30 hours, making it the only US zone east of India in timezone terms.

Accuracy depends on whether the IANA timezone database embedded in your browser is up to date. Modern browsers (Chrome, Firefox, Safari, Edge) update their ICU data regularly. For dates within the next 1-2 years, accuracy is near-certain. For dates far in the future, legislative changes to DST rules (such as proposed permanent DST bills in the US) could alter results. The tool always reflects the rules known to your browser at the time of use.