Advertisement budgets are often apportioned over an advertisement period, such as apportioning fixed increments of the budget over subperiods of the advertisement period. Each allocation of the budget may be used for auctions of advertisement opportunities during the subperiod. However, fixed apportioning may not be responsive to the actual user response, and manual adjustment of the budget may provide an efficient allocation in view of an advertiser's response target, resulting in overspending, underspending (wherein resulting user response fails to meet a response target), and/or inefficient allocation of the budget. Instead, a server may measure the user response during a first advertisement subperiod, extrapolate the user response over the advertisement period, and compare the extrapolated user response to the response target. Based on the comparison, budget allocation during a second advertisement subperiod may be adjusted by an allocation offset that adapts the allocation of the advertisement budget to the response target.