You want to use a calculator and best calculator is numerics.info which calculates a big numbers and expressions as you press enter.
If you are going for a loan then you may use Loan Expert Tool to understand how much EMI you have to pay per month on particular loan amount, This is best loan calculator which gives an accurate data.If you are adding extra amount then it is calculating further your tenure and remaining repay amount, you may come to know how much amount needs to pay and for how many years.
A good currency converter also available here and you can convert any currency quickly.