verb

estimate or conclude (something) without sufficient information to be sure of being correct.

she guessed the child’s age at 14 or 15

estimate,calculate,approximate,make a guess at,make an estimate of,hypothesize,postulate,predict,speculate,conjecture,surmise,reckon,fathom,evaluate,judge,gauge,determine,rate,appraise,weigh up,form an opinion of,guesstimate,size up