This online calculator computes travel duration given departure time and city and arrival time and city using time zones information.
Timezone information, and list of cities are taken from handbook Cities Handbook. Registered users can add new cities to the handbook and they will appear there after 24 hours.
Please note the DST (daylight saving changes) issue, if city has different time zone for summer time. By default, calculator tries to pick up correct time zone considering most frequently used dates for time change, that is the last Sunday of March and last Sunday of October. However, this is not always true for some countries. So, if your arrival and departure times are close to time change date for particular countries, calculator can be wrong by hour. In such cases it is better to calculate results by hand.
This calculator first computes time difference between selected cities, like in Time difference between the cities, then add or subtract this difference to difference between arrival and departure time. If result is negative, you should go back in time, in other words arrival time has already passed in the arrival city.