misrepute
misestimate
misfigure
misevaluate
misforecast
miscalculate
under the impression
misaccount
misassess
misconclusion
overreckoning
overestimation
overrating
put two and two together and make five
overestimate
misextrapolate
mispredict
misprediction
misprognosticate
overprediction
erroneousness
misquantify
miscompute
misproportion
highball
misestimation
malobservation
misconstrue
fallibility
mismeasure
misconstruct
eat crow
reverse jinx
stretch
undetermine
misinference
misdigest
misinterpret
overrate
misdeclare
underestimation
underestimate
mispredictor
misdetermine
misascribe
underreckoning
off target
estimation
underrating
miss one's guess