The standard calendar followed across India is the Gregorian calendar, which is the same as the internationally used calendar. It is the official civil calendar used for all government purposes, daily activities, and business operations throughout the country, including both in the North and South of India.

The standard calendar followed across India is the Gregorian calendar, which is the same as the internationally used calendar. It is the official civil calendar used for all government purposes, daily activities, and business operations throughout the country, including both in the North and South of India.

However, India has several traditional calendars based on regional customs, religious practices, and cultural influences, with each region following its own version for specific festivals, agricultural events, and religious observances. These include:

1. Vikram Samvat – Widely used in North India, it is a lunar-solar calendar that starts in the month of Chaitra (March-April) and is followed in states like Rajasthan, Gujarat, and Uttar Pradesh.

2. Shaka Samvat – The official calendar of the Government of India, it is primarily used in Maharashtra and Karnataka and starts in the month of Chaitra (March-April).

3. Tamil Calendar – Used in Tamil Nadu, it is a solar calendar that begins with the month of Chithirai (mid-April).

4. Bengali Calendar – Primarily used in West Bengal, it starts in the month of Baishakh (mid-April).

5. Telugu Calendar – Followed in Andhra Pradesh and Telangana, it is a lunar calendar that starts with the month of Chaitra (March-April), with Ugadi being the New Year.

6. Malayalam Calendar – Used in Kerala, it is based on the solar cycle and begins with the month of Medam (April-May).

Each of these regional calendars is important for cultural, agricultural, and religious purposes, with festivals like Diwali, Holi, and various New Year celebrations falling according to the respective regional calendar. However, the Gregorian calendar is the standard and official calendar for all civil, government, and administrative purposes across the entire nation.