Add up your zakatable wealth (cash, gold of any karat, silver, goods for sale, money owed to you and investments), deduct debts due now, and compare the total with the nisab. If it reaches the nisab, zakat of 2.5% is shown in figures and in Arabic words.
The minimum wealth on which zakat is due: the value of 85 grams of pure gold, or 595 grams of silver. Many people use the gold nisab; the silver nisab is lower and more cautious.
By its pure-gold content: 21 karat counts as 21/24 of the 24-karat price, 18 karat as 18/24, and so on.
Zakat is 2.5% per lunar year. A Gregorian year is about 11 days longer, so 2.5775% gives the same result for people who calculate on a Gregorian date.
No. It's a calculator to help you organise the figures. For your own situation, ask a trusted scholar.