An Etymological Dictionary of the German Language/Annotated/rechnen

rechnen, verb, ‘to reckon, estimate, deem,’ from Middle High German rëchennen, Old High German rëhhanôn, ‘to count, reckon, render an account’ (ë is proved by modern dialects). The assumed Gothic *rikanôn, which is also implied by Anglo-Saxon rëconian, English to reckon, and likewise the equivalent Low German and Dutch rekenen, is abnormally represented by the strange word rahnjan. The West Teutonic *rëkanôn is connected, probably in the sense of ‘to compute, collect’ (compare the meanings of lesen), with the root rak, ‘to collect’ (see Rechen), to which Anglo-Saxon ręččan (from rakjan), ‘to count up, compute, arrange,’ and Anglo-Saxon racu, Old Saxon raka, Old Icelandic rahha, feminine, ‘speech, account, affair,’ also belong; so too geruhen.