Subtract nine and a half hours, or ten and a half
India Standard Time is fixed at UTC+5:30 all year. The United States is not, so the amount you subtract depends on the American date: 9 hours 30 minutes while the US is on daylight saving, and 10 hours 30 minutes through the American winter.
Your evening is their morning
From Bengaluru, Mumbai, Delhi or Hyderabad, the American East Coast wakes up as your working day ends. A 6:30 PM call in India is 9:00 AM in New York during US summer. Push to 8:00 PM your time and you catch their mid-morning. Anything before about 5:00 PM in India lands before the American working day has started.
The two dates you should put in your calendar
Nothing changes in India, but the offset to the US shifts on the second Sunday in March and the first Sunday in November. For a recurring call fixed in Indian local time, the American end silently moves by an hour twice a year. Recurring meetings created in the wrong zone are the classic casualty: the invite holds its Indian hour and quietly drifts for everyone in New York.
Watch the abbreviation
IST is also used for Irish Standard Time and Israel Standard Time. If you are writing to a mixed audience, name the city or give the UTC offset. Half-hour offsets are unusual enough that people also tend to round them away, so spell out the thirty minutes.