verb
-ons; -oned; -oning
[+ obj] informal :to think or suppose (something) :to believe that (something) is true or possible
to calculate or guess (an amount, number, value, etc.) :to have or form a general idea about (something)
to think of (someone or something) as being something specified - usually used as (be) reckoned
reckon on
[phrasal verb]
reckon on (something) :to expect (something) to happen :to plan on (something)
reckon up
[phrasal verb]
reckon up (something) or reckon (something) up chiefly Brit :to calculate the total number or amount of (something)
reckon with
[phrasal verb]
reckon with (something) :to consider or think about (something) when you are making plans
reckon with (someone or something) :to deal with (someone or something that can cause problems or trouble)
If you are a person/force to be reckoned with or a person/force to reckon with, you are someone who is strong and cannot be ignored.
reckon without
[phrasal verb]
reckon without (something or someone) chiefly Brit :to fail to consider (something or someone) when making plans