To anticipate or depend on something happening or being available.
We can't reckon on the weather being good for the picnic.
ピクニックの天気が良くなると期待することはできません。
To depend on someone or something to perform an action or be a certain way.
You can reckon on her to be late; she's never on time.
彼女が遅れると期待できます;彼女は決して時間通りではありません。