An approach is provided for speculative navigation routing in incomplete maps. The approach involves, for example, generating an offline navigation route to a destination using offline map data cached at a device. The approach also involves transmitting a routing request to a routing server for an online navigation route to the destination. The approach further involves providing the online navigation route or a portion of the online navigation route based on determining that the online navigation route or the portion of the online navigation is received within a timeout period. The approach further involves providing the offline navigation route or a portion of the offline navigation route generated during the timeout period based on determining that the online navigation route or the portion of the online navigation route is not received before the timeout period ends.