What is the IST to PST Converter?
This tool converts a time given in India Standard Time (IST, UTC+5:30) to Pacific Standard Time (PST, UTC−8:00). The fixed offset between the two zones is exactly 13 hours and 30 minutes, so the rule is simply PST = IST − 13.5 hours. Note: PST is the winter (standard) time on the US/Canada Pacific coast. During daylight saving (PDT, UTC−7) the gap shrinks to 12.5 hours — this calculator uses the standard PST offset.
How to use it
Enter the IST hour using a 24-hour clock (0–23) and the minute (0–59). The calculator subtracts 13 hours 30 minutes and shows the matching PST time, along with a note telling you whether the result lands on the previous, same, or next calendar day.
The formula explained
We first express IST as minutes after midnight: \(t = \text{hour} \times 60 + \text{minute}\). We subtract 810 minutes (\(13.5 \times 60\)). Because the result can be negative or exceed a day, we wrap it with a modulo-1440 operation to keep it inside a single 24-hour window, and track the day offset separately.
$$\text{PST}_{\min} = \left(\left(\left(60\cdot\text{IST Hour} + \text{IST Minute}\right) - 810\right) \bmod 1440 + 1440\right) \bmod 1440$$where
$$\begin{gathered} \text{PST}_{\min} = \Big(\big(T - 810\big) \bmod 1440 + 1440\Big) \bmod 1440 \\[1.5em] \text{where}\quad \left\{ \begin{aligned} T &= 60\cdot\text{IST Hour} + \text{IST Minute} \\ \text{PST Hour} &= \left\lfloor \tfrac{\text{PST}_{\min}}{60} \right\rfloor \\ \text{PST Minute} &= \text{PST}_{\min} \bmod 60 \end{aligned} \right. \end{gathered}$$
Worked example
Suppose it is 10:30 IST. In minutes: \(10\times60 + 30 = 630\). Subtract 810 → \(-180\). Wrapping: \((-180 + 1440) = 1260\) minutes = 21 hours 0 minutes. So 10:30 IST = 21:00 (9:00 PM) PST on the previous day.
FAQ
How many hours is IST ahead of PST? IST is 13 hours 30 minutes ahead of PST.
What about daylight saving (PDT)? When the Pacific zone observes PDT (UTC−7), the difference is 12 hours 30 minutes. This converter assumes standard PST.
Why does the date sometimes change? Because of the large 13.5-hour offset, an IST morning often corresponds to the previous evening in PST.
