A visa is valid for a limited period. On the visa sticker in your passport you can find information about during which period the visa is valid, how many days you are allowed to stay in the Schengen area and how many times you are allowed to enter the Schengen are during the validity period. A visa that allows a foreign national to enter the Schengen states may be issued for up to five years, allowing a stay of maximum 90 days during a period of 180 days. To check how many days you have left, please use the Schengen calculator. Your visa application should clearly state the number of days and entries that you need. The length of the stay and the purpose of the trip must correspond. See Annex A attached.
In case you are issued a single-entry visa, 15 days are automatically added to the length of your stay. These days are meant to allow you to use your visa even if unforeseen exceptional circumstances occur. However, you are only allowed to stay in the Schengen area for the number of days indicated, within the period specified on your visa sticker.