Source : Webster's Revised Unabridged Dictionary (1913)

Overrate \O`ver*rate"\, v. t. [imp. & p. p. {Overrated}; p. pr.
   & vb. n. {Overrating}.]
   To rate or value too highly.

Source : WordNet®

overrating
     n : a calculation that results in an estimate that is too high
         [syn: {overestimate}, {overestimation}, {overreckoning}]