reck·on 
/ˈrɛkən/ verb
reck·ons; reck·oned; reck·on·ing /ˈrɛkən/ verb [+ obj] 1 informal : to think or suppose (something) : to believe that (something) is true or possible
▪ I reckon that we'll have to leave early. ▪ Do you reckon you'll be able to go to the grocery store after work? ▪ We'll have to leave early, I reckon. ▪ “Do you think it will rain?” “(I) Reckon so.” [=I think it will] 2 : to calculate or guess (an amount, number, value, etc.) : to have or form a general idea about (something)
▪ They reckoned that they would reach their destination by noon. ▪ I reckon [=estimate] the height of the building to be 70 feet. ▪ Losses were reckoned to be over a million dollars. 3 : to think of (someone or something) as being something specified — usually used as (be) reckoned ▪ She was reckoned [=considered] to be among the group's leaders. = She was reckoned as one of the group's leaders.
▪ I reckon that we'll have to leave early. ▪ Do you reckon you'll be able to go to the grocery store after work? ▪ We'll have to leave early, I reckon. ▪ “Do you think it will rain?” “(I) Reckon so.” [=I think it will]
▪ They reckoned that they would reach their destination by noon. ▪ I reckon [=estimate] the height of the building to be 70 feet. ▪ Losses were reckoned to be over a million dollars.
reckon on [phrasal verb]
reckon on (something) : to expect (something) to happen : to plan on (something)
▪ The train was an hour late, which was something we hadn't reckoned on. ▪ She reckoned on winning the election. [=she expected to win the election]
▪ The train was an hour late, which was something we hadn't reckoned on. ▪ She reckoned on winning the election. [=she expected to win the election]
reckon up [phrasal verb]
reckon up (something) or reckon (something) up chiefly Brit : to calculate the total number or amount of (something)
▪ He reckoned up the bill.
▪ He reckoned up the bill.
reckon with [phrasal verb] 1 reckon with (something) : to consider or think about (something) when you are making plans
▪ They hadn't reckoned with all the paperwork that went along with buying a new house. 2 reckon with (someone or something) : to deal with (someone or something that can cause problems or trouble)
▪ Anyone who tries to change the system will have to reckon with me. = Anyone who tries to change the system will have me to reckon with. [=I will oppose/fight anyone who tries to change the system] ◊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.
▪ When he won his first three matches, the other players realized that he was a force/man to be reckoned with.
▪ They hadn't reckoned with all the paperwork that went along with buying a new house.
▪ Anyone who tries to change the system will have to reckon with me. = Anyone who tries to change the system will have me to reckon with. [=I will oppose/fight anyone who tries to change the system] ◊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.
▪ When he won his first three matches, the other players realized that he was a force/man to be reckoned with.
reckon without [phrasal verb]
reckon without (something or someone) chiefly Brit : to fail to consider (something or someone) when making plans
▪ They thought they could defeat him, but they reckoned without his determination.
▪ They thought they could defeat him, but they reckoned without his determination.
