to get a total by counting that is smaller than the actual total of
the act or an instance of undercounting
transitive verbun·der·count·ed, un·der·count·ing, un·der·counts
To record fewer than the actual number of (persons in a census, for example).
(third-person singular simple present undercounts, present participle undercounting, simple past and past participle undercounted)
under- +"Ž count