A tolerance band is determined for an online advertisement campaign. The tolerance band defines upper and lower bounds on acceptable deviation from a cumulative linear advertisement delivery goal for the length of the campaign and may be employed to manage delivery of advertisement impressions during the campaign. The upper and lower bounds of tolerance band may flatten with time: acceptable deviation is generally higher at the beginning of the campaign and is lower as the campaign approaches its end date. The tolerance band may be employed to modify a periodically-determined delivery quota for an advertisement line based on the current performance of the advertisement line in relation to its tolerance band. An advertisement line that has fallen below the lower bound may get higher delivery priority relative to other advertisement lines so that it may be given more delivery opportunities. An advertisement line that is delivering above the upper bound may have its quota reduced, possibly to zero, and get lower delivery priority.