Question: I was wondering about prices of visa extentions in iran for one adult and two children, I know it changes depending on how long you want the extension for.

Answer: Iran visa extension is normally quite straightforward actually, for that you need to go the nearest Police Department of Alien Affairs before your visa expires. There you will be asked for the reasons of your request for an extension.
In 1 or 2 days against paying about 10 or 20 dollars the visa can easily be extended in Tehran, Shiraz, Esfahan, Yazd and other touristy cities. Shiraz is the best place and has the most helpful staff.
In Shiraz you should go to the Police Department of Alien Affairs at Kaveh Street, Vali Asr Sq. and ask for an extension. And in Tehran you should go to Sepah Sq., Pol-e-Choobi, Enghelab Ave.

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