A K-1 fiance visa lets the fiancé or fiancée of a U.S. citizen enter the United States on the condition that the couple gets married no more than 90 days later. For terminology purposes, the fiancé is used to refer to either a male or female partner who is engaged.

The sponsor must be a U.S. citizen.
The relationship between the couple must be proved through evidence such as but not limited to photos, emails or letters, statements, etc.
In addition, the couple must be able to provide evidence of them having met in person at least once within two years preceding the filing of the visa form. This requirement may be overlooked in certain extreme cases, such as in circumstances where physical meetings would violate social norms.
Both partners must currently be unmarried. Previous annulments, death certificates or divorce decrees must be produced to indicate the end of any previous marriages.
Both partners have to give a signed statement showing their intention to marry within 90 days of the fiancé’s arrival in the United States.
Income requirement for the partner who is a U.S. citizen: The adjusted gross income on their most recent tax return must at least meet the Federal Poverty Guidelines.
Note: If this is the only requirement that is unmet, a joint financial sponsor must provide an “affidavit of support.”