Total = swap × lots × (nights + 2 × triple days). A negative rate is a cost, a positive one a credit. Rates are your broker's, change with interest rates, and differ long versus short.
About this calculator. The result is an educational estimate. Contract sizes, pip values, spreads, commissions and overnight financing differ by broker and by instrument, and fills can differ from the prices you model. Check your own account's specification before trading.