The number of runs by which a team must lead to enforce follow-on upon its opponent is determined by Law 13 of the Laws of cricket, which takes the length of the match into consideration:
* In a match of five days or more, a side which bats first and leads by at least 200 runs has the option of requiring the other side to follow-on.
* in one of three or four days, 150 runs;
* in a two-day match, 100;
* in a one-day (two-inning) match, 75.
Where a match is shortened, the leads required to have the option of enforcing the follow-on are determined by how many days' (or part-days') play remain when the match starts. For example, suppose a match is scheduled for five days, but the first day is washed out because of rain. If the match then begins on the second scheduled day of the match, the team batting first needs a first innings lead of 150 runs or more to have the option of enforcing the follow-on. This only applies to time lost before the first ball has been bowled: if a five-day match starts on the scheduled first day but, say, the second day is completely lost, it still counts as a five-day match for the purposes of calculating the follow-on target.
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