Timezone Calculator
EverydayCalculate the time difference between any two time zones. Find out how many hours ahead or behind a city is, including India's IST offset from major world cities.
Timezone 1 (From)
Timezone 2 (To)
Time Difference
0h
EST is the same time as IST
Timezone 1
IST
+0:00
Timezone 2
EST
+0:00
What is a Timezone?
A Timezone Calculator calculates the time difference between two time zones — how many hours and minutes one zone is ahead of or behind the other, plus each zone's offset from UTC (Coordinated Universal Time). It is the essential tool for scheduling international meetings, coordinating remote teams, and understanding world time relationships.
The calculator uses your device's Intl.DateTimeFormat API to determine each timezone's current UTC offset, automatically accounting for Daylight Saving Time changes. This means the result reflects the actual current difference, not a static nominal offset — New York's offset from IST is 10:30h in winter and 9:30h in summer because New York observes DST while India does not.
The 25 included time zones cover every major business region: North America (EST, CST, MST, PST, Alaska, Hawaii), South America (BRT), Europe (GMT, CET, EET, MSK), Middle East (GST), South Asia (IST, PKT), Southeast and East Asia (BST, ICT, SGT, CST, JST, KST), Oceania (AEST, NZST), and Africa (WAT, EAT).
For converting a specific date and time from one timezone to another, use the Timezone Converter. For calculating the number of days between two dates, use the Date Difference Calculator.
How to use this Timezone calculator
- Select Timezone 1 (From) — the reference timezone (e.g., IST for an India-based user).
- Select Timezone 2 (To) — the timezone you want to compare against.
- The Hour Difference shows instantly — positive means TZ2 is ahead of TZ1, negative means it is behind.
- Check the Minute Component — if non-zero, the offset includes a fractional hour (as with India, Iran, or Nepal).
- Use the UTC Offsets to independently verify both zones' positions on the global timeline.
- For detailed conversion of a specific time, visit the Timezone Converter.
Formula & Methodology
UTC Offset extraction: The calculator formats a fixed reference date usingIntl.DateTimeFormatwith each timezone and computes the difference from the UTC representation of that same instant. This captures the current offset including any DST in effect. Net offset:Net Offset (minutes) = UTC_Offset(TZ2) − UTC_Offset(TZ1)Decomposition:Hours = floor(|Net Offset| ÷ 60)with sign;Minutes = |Net Offset| mod 60with sign IST offset reference table (common pairs): | City | Local timezone | IST offset | |---|---|---| | London (winter) | GMT (UTC+0) | −5h 30m | | London (summer) | BST (UTC+1) | −4h 30m | | Dubai | GST (UTC+4) | −1h 30m | | Singapore | SGT (UTC+8) | +2h 30m | | Tokyo | JST (UTC+9) | +3h 30m | | Sydney (winter) | AEST (UTC+10) | +4h 30m | | New York (winter) | EST (UTC-5) | −10h 30m | | New York (summer) | EDT (UTC-4) | −9h 30m | | San Francisco (winter) | PST (UTC-8) | −13h 30m | | San Francisco (summer) | PDT (UTC-7) | −12h 30m |
Frequently Asked Questions
What is a Timezone Calculator?
A Timezone Calculator tells you the time difference between any two time zones — how many hours (and minutes) one is ahead of or behind the other. Unlike a clock or world time app, it shows the structural offset that drives the difference, including fractional offsets like India's unique +5:30. It also shows each timezone's UTC offset, which is the foundation for all conversions.
Why does India have a 30-minute offset (+5:30)?
India Standard Time (IST) is UTC+5:30, a half-hour offset chosen to compromise between its eastern and western extents while aligning roughly with the solar noon across the country. India chose not to split into multiple time zones (despite spanning nearly 30 degrees of longitude) to maintain administrative and railway uniformity. Sri Lanka (UTC+5:30) and Nepal (UTC+5:45, the rarest offset) have similar fractional offsets in the region.
How many hours is IST ahead of EST (New York)?
India Standard Time (IST, UTC+5:30) is 10 hours 30 minutes ahead of US Eastern Standard Time (EST, UTC-5) in winter. During US Daylight Saving Time (EDT, UTC-4), the difference narrows to 9 hours 30 minutes. India does not observe Daylight Saving Time — its UTC+5:30 offset is fixed year-round. This half-year shift of one hour matters for scheduling recurring calls between India and the US East Coast.
What is UTC and why is it the reference point?
Coordinated Universal Time (UTC) is the primary global time standard maintained by atomic clocks and is the successor to Greenwich Mean Time (GMT). All time zones are defined by their offset from UTC (e.g., IST = UTC+5:30, PST = UTC-8). UTC has no daylight saving time adjustment, making it the stable reference for computing time differences. UTC itself is not tied to any country's administrative time.
What is Daylight Saving Time and which countries observe it?
Daylight Saving Time (DST) is the practice of advancing clocks by one hour during summer months to shift an hour of daylight from early morning to evening. Major DST-observing regions include the US, Canada, most of Europe, and Australia. India, China, Japan, and most of Africa and Southeast Asia do not observe DST. When DST shifts in the US (second Sunday of March and first Sunday of November), the offset between IST and US time zones changes by one hour.
How is the time difference calculated between two cities?
The time difference equals the difference in UTC offsets of the two time zones. If City A is UTC+5:30 and City B is UTC-5:00, the difference is 5:30 − (−5:00) = +10:30 hours (City A is 10 hours 30 minutes ahead of City B). The calculator uses Intl.DateTimeFormat to determine each timezone's current UTC offset, accounting for any DST that is in effect.
Why do the offsets change at different times of year?
When a timezone observes Daylight Saving Time, its UTC offset changes by +1 hour during summer. For example, New York moves from UTC-5 (EST) in winter to UTC-4 (EDT) in summer, changing the IST-New York difference from 10:30h to 9:30h. The calculator always uses the current offset, so it accurately reflects the real-time difference at the moment of calculation.
What is the best time to schedule a meeting between India and the US West Coast?
IST is UTC+5:30, and PST (California winter) is UTC-8, making the difference 13:30 hours. A 9:00 AM meeting in San Francisco corresponds to 10:30 PM in India — outside normal working hours. The minimal overlap is 8:00–9:00 PM IST (6:30–7:30 AM PST), which requires early morning commitment from the US side. During US summer (PDT, UTC-7), this becomes 8:00 PM IST = 7:30 AM PDT — slightly more workable.
Is this calculator the same as the Timezone Converter?
They have different purposes. The [Timezone Converter](/timezone-converter/) takes a specific datetime and converts it from one timezone to another — useful when you know 'it's 3:30 PM in London; what time is that in Singapore?' This calculator focuses on the structural time difference (offset) between two zones and their UTC offsets — useful when you need to understand the relationship between two zones to plan schedules.
Why does the calculator show 'Minute Component of Offset' separately?
Most timezone differences are whole hours, but several important timezones have fractional offsets: India (+5:30), Nepal (+5:45), Iran (+3:30), Afghanistan (+4:30), Sri Lanka (+5:30), Myanmar (+6:30), and the Chatham Islands (+12:45). Showing hours and minutes separately makes these fractional offsets immediately clear and prevents rounding errors when scheduling meetings.