To calculate or estimate something. I reckon the total cost will be around $200.
To consider or regard in a specified way. She is reckoned to be one of the best players in the league.
To rely on or be sure of something. You can reckon on me to help you with the project.
(chiefly British, informal) To think, suppose or believe. I reckon we'll get there before it gets dark.
(with "with") To take into account or deal with; confront. They didn't reckon with the sudden change in weather.