To reckon means to think, believe, or suppose something based on your judgment. When your friend says “I reckon it'll rain today,” she's making a considered guess based on the dark clouds overhead. When a teacher says “I reckon you studied hard for this test,” he's forming an opinion from the quality of your answers.

The word has a relaxed, confident feel to it, like someone who's thought things through and reached a conclusion without needing absolute proof. You might say “I reckon we have enough time to finish the project” or “She reckons the trail will take two hours.”

Reckon can also mean to calculate or figure something out mathematically. Sailors used to reckon their position at sea by measuring the stars, and accountants reckon up totals when balancing books. When someone says “by my reckoning,” they mean “according to my calculations” or “the way I figure it.”

The phrase to be reckoned with describes someone or something powerful that can't be ignored. A chess player who wins tournament after tournament is a force to be reckoned with. The expression suggests respect, sometimes mixed with caution, like recognizing that a challenge ahead won't be easy.