What is the value of my coin?

Your image is, unfortunately, too dark to show the details. This website has photos and descriptions of many thousands of coins from all over the world. This link should take you to the India section: http://worldcoingallery.com/countries/India1.php It is necessary to know which State or Princedom the coin was issued for. If the date is really 1818, it is not likely to be in Arabic numerals. You should be aware that there are a number of fakes and forgeries around - see this article: http://kulraj-the-numismatist.blogspot.com/2009/02/east-india-company-coins.html - but the site above should be able to tell you what you need to know. There is another picture I found here: http://kolkata.olx.in/1818-east-india-half-anna-coin-of-ram-sita-laksman-and-hanuman-iid-80322168 of an 1818 half-Anna. It doesn't look quite the same as yours but the seller wants 500,000 Rs (!)