The Collaborative International Dictionary
Misreckon \Mis*reck"on\, v. t. & i.
To reckon wrongly; to miscalculate.
--Swift.
Wiktionary
vb. 1 (context transitive English) To add (something) up incorrectly, make a wrong calculation of (an amount etc.). 2 (context reflexive obsolete English) To make a wrong calculation, to be in error.
Usage examples of "misreckon".
And before you misreckon, I came to Orion Lake strictly to relax and unwind.
But in her topographical ignorance as a late comer to the place, she misreckoned the distance of her journey as not much more than half what it really was.
It was Trade Day, unless he'd misreckoned, and by noon he had a good chance of finding his uncles along the river front.
When Kantos Kan told me, I realized with a pang of dismay that I had misreckoned the time while I lay in the utter darkness of my cell.