Does the time difference between New Delhi and Singapore change during the year?

No. The gap stays at 2h 30m all year.

When is the best time to call Singapore from New Delhi?

Between 09:00 and 14:30 in New Delhi, which is 11:30 to 17:00 in Singapore.

New Delhi is 2h 30m behind Singapore. This gap is the same all year — neither city shifts its clocks relative to the other.

New Delhi

India

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Singapore

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A 9-to-5 day in each city overlaps for 5h 30m. That is 09:00–14:30 in New Delhi, which is 11:30–17:00 in Singapore.

City	Time zone	UTC offset
New Delhi · India	Asia/Kolkata	UTC+5:30
Singapore · Singapore	Asia/Singapore	UTC+8

What is the time difference between New Delhi and Singapore?: New Delhi is 2h 30m behind Singapore. This gap is the same all year — neither city shifts its clocks relative to the other.
Does the time difference between New Delhi and Singapore change during the year?: No. The gap stays at 2h 30m all year.
When is the best time to call Singapore from New Delhi?: Between 09:00 and 14:30 in New Delhi, which is 11:30 to 17:00 in Singapore.