Everyone except nationals of Bhutan, Maldives and Nepal needs a visa to visit India.

Tourist visas are valid for six months from the date of issue, and cost around US$50. Processing takes from one day to one week

Visas need to be applied for online before you visit an embassy.

A visa on arrival is available for tourists from Cambodia, Finland, Indonesia, Japan, Laos, Luxembourg, Myanmar, New Zealand, Philippines, Singapore and Vietnam.
The on arrival visa is only available at Bengaluru, Chennai, Delhi, Hyderabad, Kochi, Kolkata, Mumbai and Trivandrum airports for a fee of US$60. The visa is single entry and only valid for 30 days.

If you would like to stay in India for longer than six months, you will need to leave the country and apply for another visa. Getting another visa after you have had two in a row may prove a little difficult.
The Indian embassy in Kathmandu may be able to issue new visas but there crackdowns from time to time that may make getting a new visa near impossible.

Indian Immigration

Visa on arrival details

Indian visa online application

Indian Embassies and consulates