Locate the visa expiration date. Some visas will state "valid until date," while others will say "valid for 5 (or 10) years from the date of issuance." If there is no statement of length of validity, check whether the visa is valid for single or multiple entries. Those with a single entry are valid for only one visit after which another visa is required.
Locate the designated duration of stay listed on the visa. Some visas list the duration of stay on the visa. These lengths usually run either 30, 90, or 180 days and will likely be written both in English and in the language of the issuing nation.
Refer to the entry stamp in your passport next to your visa. Some countries do not list a designated duration of stay on the visa itself. In such cases, you will be given one upon entry into the country. In the United States, this is the I-94 stamp card placed in your passport at the port of entry by a customs officer. The date listed in the lower right-hand corner is the date upon which your stay expires and you must leave. The placement and type of stamp stating the duration of stay varies per country, but it will usually be located on the page opposite your visa.