In October 2015, Iran has granted visa upon arrival to 58 nations, and it’s recent news that they are starting to issue 30-day visas to 180 nationalities, so you are likely to be fine, but just to make sure you don’t have unpleasant surprises, get in touch with the Iranian embassy in your country to check their visa requirements. I have devoted a post to the process of getting Iran visa, the different requirements depending on your nationality and what papers you need should you apply at the embassy in your country or at the airport upon arrival.