noun which may take the genitive case particle 'no'
not factored in; unaccounted for; unplanned for
Describes something that was not included in a plan, calculation, or expectation. Often used with ～の or as a noun.
交通費は計算外の出費だった。
The transportation cost was an unplanned expense.
彼の反応は計算外だった。
His reaction was unexpected.
想定外 means 'beyond assumptions' or 'unforeseen', often used in formal contexts like disaster planning. 計算外 is more about personal plans or calculations.
Compound of 計算 (calculation) and 外 (outside). Literally 'outside the calculation'.