계산해주세요 can be used in the two situations.
1. You can see 계산해주세요 ( meaning 'to calculate') in the academic, mathematics and business situations such as (이 문제를) 계산하세요, (매출 금액이 맞는지) 계산해 주세요?
2. On the other hand, 계산해주세요 (to pay) also can be used in the situations where you're actually buying somethings in the stores or restaurants etc.
Example : (이 물건 값을) 계산해 주세요,
(밥 값을) 계산해 주세요.
As you already know, subject or object word easily can be skipped in spoken Korean.
Hope it helps you ;)