Methods, systems and computer program products for submitting a network proxy bid and replacing the network proxy bid with an actual bid associated with advertisement placement are described. In some implementations, instead of submitting a static bid, an advertiser can submit a network proxy bid to an advertising exchange. A network proxy bid can indicate to the advertising exchange that the advertiser wishes to receive a call back from the advertising exchange when an impression matching targeting criteria specified by the advertiser becomes available. The advertiser then can calculate and submit an actual static bid to replace the network proxy bid in response to the call back.