Unlimited number of immigration visas is provided only for immediate relatives of the US Citizen spouses and unmarried children under the age of 21.The rest of relatives are divided in the following categories:
- First preference is given to unmarried children of US Citizen who are older than 21.
- Second preference is given to spouses and unmarried (under 21) children of Legal Permanent Residents.
- Third preference is given to married children of US Citizens.
- Fourth preference is given to brothers and sisters of US citizens that are older than 21.
The total number of family based visas is determined by the following calculation: 480,000 minus the number of immediate relatives (and children born to Legal Permanent Residents) that were allowed in the US in a previous fiscal year, plus the number of the unused employment based visas from the previous fiscal year.