What is the GMT to IST Converter?
This tool converts a time given in GMT (Greenwich Mean Time) to IST (India Standard Time). India observes a single time zone year-round, fixed at UTC/GMT +5:30. There is no daylight saving time in India, so the offset is always exactly 5 hours and 30 minutes ahead of Greenwich.
How to use it
Enter the GMT hour (0–23) and minute (0–59). The calculator adds 5 hours and 30 minutes and returns the equivalent IST time. If the result crosses midnight, the tool shows a day offset (next day or previous day) so you always know which calendar day applies.
The formula explained
The conversion is simply IST = GMT + 5:30. Internally we convert the GMT time to total minutes since midnight, add 330 minutes (\(5\times60 + 30\)), then convert back to hours and minutes. If the total reaches 1440 minutes (24 hours) or more, one day is subtracted and the day offset is incremented.
$$\text{IST}_{\text{total}} = \left( 60 \times \text{GMT Hour} + \text{GMT Minute} + 330 \right) \bmod 1440$$
$$\text{where}\quad \left\{ \begin{aligned} \text{IST Hour} &= \left\lfloor \dfrac{\text{IST}_{\text{total}}}{60} \right\rfloor \\ \text{IST Minute} &= \text{IST}_{\text{total}} \bmod 60 \end{aligned} \right.$$
Worked example
Suppose it is 20:00 GMT. In minutes that is \(20\times60 = 1200\). Adding 330 gives 1530 minutes. Since \(1530 \ge 1440\), subtract 1440 to get 90 minutes and a day offset of +1. 90 minutes is 1:30. So 20:00 GMT = 01:30 IST the next day.
FAQ
Is IST the same as UTC+5:30? Yes. For practical purposes GMT and UTC are treated as identical, and IST is exactly +5:30 from both.
Does India use daylight saving time? No. India keeps a constant offset of +5:30 all year, so this conversion never changes seasonally.
Why does the result sometimes show "next day"? Because adding 5:30 can push the time past midnight. The day offset tells you whether the IST time falls on the same, next, or previous calendar day.
