Time Zone Converter Calculator
Converts a clock time from one UTC offset to another, with optional daylight saving adjustment. Use it when scheduling international meetings, coordinating remote teams, or planning cross-timezone travel.
Last updated: September 2026
Formula below · 2 sources (usgs.gov, Wikipedia) · Updated Sep 2026
Compare with similar
About this calculator
Every time zone is defined by its offset from Coordinated Universal Time (UTC). To convert a source time to a target time zone, shift it by the difference between the offsets: targetTime = sourceTime + (targetOffset − sourceOffset) + dstAdjustment. The calculator works in minutes so that the minutes field is carried through: result = (hour × 60 + minute + (toOffset − fromOffset) × 60 + dstAdjustment × 60) mod 1440, with a second modulo so that negative intermediate values wrap correctly into the 0–1439 range. The result is minutes since midnight in the target zone — divide by 60 for the hour and take the remainder for the minutes (1170 = 19:30). The offsets in the menus are standard-time offsets. If the destination is on daylight saving time its clock is one hour ahead, so choose +1; if the origin is on daylight saving time its local clock is one hour ahead of standard, so choose −1; if both or neither are on DST, choose Standard Time. All hours are in 24-hour format, and the date change is not shown.
How to use
Convert 14:00 (2 PM) New York time in summer (EDT, i.e. EST plus one hour of daylight saving) to Tokyo time (JST, no DST). Enter Hour = 14, Minute = 0, From = EST (UTC−5), To = JST (UTC+9) and Daylight Saving Time = Origin on Daylight Saving (−1 hour). Calculation: (14 × 60 + 0 + (9 − (−5)) × 60 − 60) mod 1440 = (840 + 840 − 60) mod 1440 = 1620 mod 1440 = 180 minutes, i.e. 03:00 the next day in Tokyo — a 13-hour difference. In winter (Standard Time) the same 14:00 EST is 04:00 in Tokyo (240 minutes).
Frequently asked questions
How do I handle Daylight Saving Time when converting between time zones?
Daylight Saving Time shifts a zone's effective UTC offset by +1 hour during summer months. When DST is active in the source zone, increase the source offset by 1 (e.g., EST UTC−5 becomes EDT UTC−4). When DST is active in the target zone, increase the target offset by 1. The calculator's menus use standard-time offsets, so its Daylight Saving field applies the net correction: +1 when only the destination is on DST, −1 when only the origin is. Note that DST dates differ by country: the US switches in March/November while Europe switches in late March/October, creating brief periods where the offset between two zones is temporarily different.
What is the difference between UTC offset and a named time zone?
A UTC offset (e.g., +5:30) is a fixed numerical shift from Universal Time, while a named time zone (e.g., 'India Standard Time') is a political/geographic designation that includes rules for DST and historical changes. This calculator works with numeric UTC offsets, which are precise and unambiguous. Named zones can change due to government decisions — countries occasionally shift their time zone permanently. For long-term scheduling systems, it is safer to store events in UTC and convert using a time-zone database like IANA (used by most programming languages).
Why does the formula add 24 before taking the modulo when converting time zones?
When you subtract a large positive source offset from an early morning hour, the intermediate value can become negative (e.g., 2 − 5 = −3). Negative values fed into a modulo operation behave unexpectedly in many programming environments: −3 mod 24 might return −3 instead of 21. Adding 24 before the mod ensures the value stays positive for all realistic inputs where the offset difference does not exceed 24 hours, which is always true since UTC offsets range from −12 to +14. The result is then correctly wrapped into the 0–23 range.