Time Difference: New York & Sydney

Calculating the time difference between New York and Sydney is tricky, not only because both cities observe daylight saving time, but they also are on the opposite hemispheres, so one city's summer is winter for the other. Sydney is GMT +1000 and New York is GMT -0500, yet the time difference between the two cities is rarely 15 hours.

For New York, DST is observed from the second Sunday in March to first Sunday in November. For Sydney, DST is observed from the first Sunday in October to the first Sunday in April. For the sake of convenience, the four relevant Sundays for 2013 are as follows: March 10, Nov 3, Oct 6, and April 7, respectively.

Sorting the dates by groups:

• Jan 1 to March 10: Sydney on DST, New York off DST --> 16 hour difference
• March 10 to April 7: both on DST --> 15 hour difference
• April 7 to Oct 6: Sydney off DST, New York on DST --> 14 hour difference
• Oct 6 to Nov 3: both on DST --> 15 hour difference
• Nov 3 to Dec 31: Sydney on DST, New York off DST --> 16 hour difference

In all, for only 56 days of the year is the time difference between New York and Sydney actually 15 hours.

Sources:

• http://wwp.greenwichmeantime.com/time-zone/rules/usa/
• http://australia.gov.au/about-australia/our-country/time