Off-by-one error

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An off-by-one error or off-by-one bug (known by acronyms OBOE, OBO, OB1 and OBOB) is a logic error that involves a number that differs from its intended value by 1. An off-by-one error can sometimes appear in a mathematical context. It often occurs in computer programming when a loop iterates one time too many or too few, usually caused by the use of non-strict inequality (≤) as the terminating condition where strict inequality (<) should have been used, or vice versa. Off-by-one errors also stem from confusion over zero-based numbering.