Can someone help in building a currency converter tool in Microsoft Excel 2013

Hi, I need to develop an offline excel tool for currency conversion. As I very frequently use the conversion of currencies in my work.....one challenge is the converted values should never be lesser (in case of inaccuracy) but slightly higher will do. Also I need to update rates quarterly which are not as per internet, that is why I need to create this tool offline. So, please also help how can I update rates periodically by dragging or importing file. What format should I use for importing? Kindly help

Why exactly don't you use something that pulls from for example XE.com ?

Its as per our business requirement, cant change that.....same through the organization.

Right, well good luck with it.