India needs to score a minimum of 379 runs against England in the second innings of the first Test at the M. A. Chidambaram Stadium in Chennai to ensure visiting skipper Joe Root can't enforce the follow-on.

How is the follow-on score calculated?

Marylebone Cricket Club’s (MCC) Law 14.1.1 states “In a two-innings match of 5 days or more, the side which bats first and leads by at least 200 runs shall have the option of requiring the other side to follow their innings.”

In simpler terms, the follow-on threshold for a team batting second in a five-day red-ball game will be the difference between the first innings score of the side that batted first and 199.

However, Law 14.1.2 adds, "The same option shall be available in two-innings matches of shorter duration with the minimum leads as follows:

- 150 runs in a match of 3 or 4 days;

- 100 runs in a 2-day match;

- 75 runs in a 1-day match."

A captain shall notify the opposing skipper and the umpires of his intention and once done so, the decision cannot be changed.

India finished day three, with local lads Ravichandran Ashwin and Washington Sundar leading a spirited fightback, at 257/6. It is still 122 runs away from the follow-on threshold and trails the visitor by 321 runs.