When should you call?

India is 9 hours 30 minutes ahead of US Eastern in summer and 10 hours 30 in winter, and it never changes its own clocks, so the gap moves twice a year at the American end. In practice that puts the workable window in your morning: 8am in New York is early evening in Delhi, which is a reasonable hour for a family call and the wrong end of the day for an office. Set both ends above and the tool does this for whichever two places you actually need.

Because the gap between two places is not a constant. The two ends change their clocks on different dates, and several countries do not change at all. A converter that stores a fixed difference is wrong for months at a time. This one reads both offsets at the moment you load it, so the window you are shown is the window that applies today.

9am to 8pm where they are. That is deliberately narrower than simply being awake: it is when somebody is up and would not mind the interruption. Being conservative costs you an hour at each end. Being generous costs somebody a call at seven in the morning.

No. Nothing on this page is stored, nothing is sent anywhere, and there is no signup. Your own time zone comes from your browser's own setting rather than from your IP address, so the page never has to ask where you are.