1. A method comprising: outputting, by a computing device and for display, a graphical keyboard comprising a plurality of keys; receiving an indication of a portion of a gesture entered at a presence-sensitive display gesture to select a group of keys at least one key of the plurality of keys, the gesture comprising a plurality of portions; maintaining, by the computing device and based at least in part on the gesture, a plurality of letter chains associated with respective combined cost values, wherein each letter chain corresponds to a different group of one or more keys of the graphical keyboard; incrementally determining for the portion of the gesture, by the computing device and in response to receiving the indication of the portion of the gesture, a candidate word, wherein the determining comprises: determining, by the computing device, a group of one or more alignment points traversed by the portion of the gesture; determining, by the computing device, respective cost values for each of at least two keys of the plurality of keys, wherein each of the respective cost values represents a probability that an alignment point of the group of alignment points indicates a key of the plurality of keys; updating, by the computing device and based at least in part on at least one of the respective cost values for one or more of the at least two keys, at least one of the respective combined cost values associated with at least one of the plurality of letter chains; comparing, by the computing device, the respective combined cost values respectively associated with the plurality of letter chains; and outputting, by the computing device for display and based at least in part on the comparison of the respective combined cost values, the candidate word.