DutyCalculator offers a free Universal Import Duty & Tax Calculator that enables webmasters to seamlessly integrate our import duty & tax calculator into your website. The calculator offers import duty & tax calculations for over 72 import countries and more countries are being added. 

The plugin is based on iframe and you only have to add this line of code to your website and you are all set: 

<iframe src="http://www.dutycalculator.com/iframe-calculation/" width="550" height="401" scrolling="no" border="0" style="border-width: 0px;"></iframe>

Drop us a line to let us know that you have added it to your site! Your users can each make 10 calculations per month free of charge. If your users would like to do more calculations than that, they are referred to DutyCalculator.com.