reckon without one's host

English

reckon without one's host (third-person singular simple present reckons without one's host, present participle reckoning without one's host, simple past and past participle reckoned without one's host)

(now idiomatic, rare) To calculate one's bill without checking with the host or landlord; hence, to come to false conclusions, to miscalculate. [from 15th c.]
- 1751, [Tobias] Smollett, The Adventures of Peregrine Pickle […], volume (please specify |volume=I to IV), London: Harrison and Co., […], →OCLC:
  He had flattered himself, that this gentlewoman would decline the proposal, as she was a person seemingly of a demure disposition, who had been born and bred in the city, where such diversions are looked upon as scenes of lewdness and debauchery. For once, however, he reckoned without his host; curiosity is as prevalent in the city as at the court-end of the town […] .
- 1823 December 23 (indicated as 1824), [Walter Scott], St Ronan’s Well. […], volume (please specify |volume=I to III), Edinburgh: […] [James Ballantyne and Co.] for Archibald Constable and Co.; London: Hurst, Robinson, and Co., →OCLC:
  But hostess as she was herself, […] she reckoned without her host in the present instance.

misjudge or miscalculate