The validity of a visa is not the same as the authorized period of stay in the issuing country. The visa validity usually indicates when the alien can apply for entry to the country. For example, if a visa has been issued January 1st and expires March 30th, and the typical authorized period of stay in a country is 90 days, then the 90-day authorized stay starts on the day the passenger reaches the country, which has to be between January 1st and March 30th. The traveller could therefore stay in the issuing country until June 1st. 