You'd be disappointed if you lined up at the candy store on "free candy day," only to learn that each person was allotted just one jelly bean. Allotted means given as a share of something.
Something that's allotted is distributed, or shared, like your allotted number of pizza slices. It can also mean your share of a job; on family clean-up day, you could be allotted the task of cleaning the bathroom. The Germanic word loter, "lot" or "share," is at the root of allotted. A plus loter form the Old French aloter, "to divide into lots." When you're spelling allotted remember to double up the ls and the ts.