Proper names are usually inflected according to the same rules as other nouns. Some examples of forming genitives of proper names: Jukka : Jukan, Helsinki : Helsingin,Kekkonen : Kekkosen, Tampere : Tampereen, Ruuttu : Ruutun, Ruutu : Ruudun, Kivi : Kiven.
However, there is variation in the inflection of names. Some people prefer having their names exempted from normal rules, so that e.g. the genitive of Satu is Satun, not Sadun, even though the corresponding common name is satu : sadun (fairy tale). This means inflecting a proper name like a completely foreign word, without consonant gradation or other stem variation.
There are two reasons for inflecting names like foreign words. First, it keeps the base form of the name easily recognizable from inflected forms. Second, it may help to avoid association with the corresponding common noun. Additional variation is caused by dialects. For example, the common noun närhi (name of a bird species, jay) is inflected närhi : närhin in some dialects, as opposite to standard Finnish närhi : närhen. The same variation exists for the surname Närhi. For this name, both inflections are accepted in standard Finnish.
There is a common idea, rejected by language authorities, that a person has the right to decide the inflection of his name. In practice, a few widely known names are usually inflected according to the wishes presented by important people with such names, e.g. Ryti : Rytin, Raade : Raaden. It is, however, normatively correct to inflect the names according to general principles: Rydin, Raateen. For various reasons, publications often still honor the opinions of public persons and inflect e.g. Orpo : Orpon instead of the standard Orvon, possibly because here association with the general noun orpo (orphan) might be seen as particularly disturbing.
For Finnish given names of people, there is an official online list that describes their inflection: Etunimien taivutus. There is also a corresponding resource for surnames: Sukunimien taivutus. The situation is not stable; there have been some changes in the rules, usually in the direction of permitting alternative inflections.
In Western dialects, double consonants in proper names are often exempted from consonant gradation, e.g. Reetta : Reettalle (instead of Reetalle), Röyttä : Röyttässä (instead of Röytässä). Such forms are sometimes used even in public communication that otherwise uses standard language.