To calculate is to compute, by figuring out a mathematical equation or a situation. You can calculate your monthly student loan payments, or calculate the risk of not paying them on time.
Calculate derives from the Latin word for "count." When you calculate, you either count something up or calculate on something happening. You might be able to calculate the answer to a simple equation in your head but need a calculator to figure out a more complex problem. And when someone is calculating, they are scheming or conniving, always figuring out the fastest way to get ahead.